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Project Gutenberg Python problem?
Question: I am trying to process various texts by regex and NLTK of python -which is at
<http://www.nltk.org/book->. I am trying to create a random text generator and
I am having a hard time with a problem. First, here is my algorithm:
1. Enter a sentence as input -this is called trigger string-
2. Get longest word in trigger string
3. Search all Project Gutenberg database for sentences that contain this word -regardless of uppercase lowercase-
4. Return the longest sentence that has the word I spoke about in step 3
5. Append the sentence in Step 1 and Step4 together
6. Repeat the process. Note that I have to get the longest word in second sentence and continue like that and so on-
So far I have been able to do this for first two sentences but I cannot
perform a case insensitive search. Entire sentence database of Project
Gutenberg is available via `gutenberg.sents()` function but regex - case
insensitive search is practically impossible since the `gutenberg.sents()`
outputs the sentences in books as following -in a list of list format-:
EXAMPLE: all the sentences of shakespeare's macbeth is called by typing
import nltk
from nltk.corpus import gutenberg
gutenberg.sents('shakespeare-macbeth.txt')
into the python shell command line and output is:
[['[', 'The', 'Tragedie', 'of', 'Macbeth', 'by', 'William', 'Shakespeare', '1603', ']'],
['Actus', 'Primus', '.'], .......]
with [The Tragedie of Macbeth by William Shakespare, 1603] and Actus Primus.
being the first two sentences.
How can I find the word I'm looking for regardless of it being
uppercase/lowercase ? I'm desperately in need of help since I have been
tinkering with this for the past two days and it's starting to wear on my
nerves. Thanks a lot.
Answer: Given a list `L` of words, and a target word `t`,
any(t.lower()==w.lower() for w in L)
tells you whether L has word t in a case-insensitive way. It's faster, of
course, to do
lt = t.lower()
any(lt==w.lower() for w in L)
since Python does not "hoist" the constant computation out of the loop and,
unless you hoist it yourself, it will be performed repeatedly.
Given a list of lists `lol`, the longest sub-list including `t` can be found
by
longest = max((L for L in lol if any(lt==w.lower() for w in L)), key=len)
If multiple sub-lists include `t` and are of the same maximal length, this
will give you the first one, as it happens.
|
How do I include a Django app in my PYTHONPATH?
Question: I want to be able to import things from applications in my project without
referring to my project name.
My folder structure is like so; I have a project called djangoproject1, and
inside I have a folder called apps, and then I have my individual apps in that
folder.
djangoproject1, apps, and all my applications have an empty "__init__.py" file
in them.
In my settings.py file I have the following code:
import os
import sys
PROJECT_ROOT = os.path.dirname(__file__)
sys.path.insert(0, os.path.join(PROJECT_ROOT, "apps"))
I've tried adding my apps to INSTALLED_APPS several ways:
'djangoproject1.apps.app1', 'djangoproject1.apps.app2',
or
'apps.app1', 'apps.app2',
or
'app1', 'app2',
but nothing works. Whenever I try to do:
from app1 import *
I got an unresolved import error. I'm using the latest versions of eclipse and
django
Answer: Ok, so I got it to work by adding the apps folder to the PYTHONPATH through
eclipse under Project Properties. Is this eclipse only though? I'm not sure
how this will work when I try and deploy the site. What do you guys think?
|
What is the Python equivalent of Ruby's "inspect"?
Question: I just want to quickly see the properties and values of an object in Python,
how do I do that in the terminal on a mac (very basic stuff, never used
python)?
Specifically, I want to see what `message.attachments` are in [this Google App
Engine MailHandler example](http://pastie.org/680280) (images, videos, docs,
etc.).
Answer: If you want to dump the entire object, you can use the
[`pprint`](http://docs.python.org/library/pprint.html) module to get a pretty-
printed version of it.
from pprint import pprint
pprint(my_object)
# If there are many levels of recursion, and you don't want to see them all
# you can use the depth parameter to limit how many levels it goes down
pprint(my_object, depth=2)
Edit: I may have misread what you meant by 'object' - if you're wanting to
look at class instances, as opposed to basic data structures like dicts, you
may want to look at the
[`inspect`](http://docs.python.org/library/inspect.html) module instead.
|
What is Cloud Computing ? and Why?
Question: > **Possible Duplicates:**
> [What is Cloud computing?](http://stackoverflow.com/questions/108037/what-
> is-cloud-computing)
> [What is cloud computing?](http://stackoverflow.com/questions/1830142/what-
> is-cloud-computing)
Sorry for asking some Simple Question. But I cannot clearly understand the
needs of Could Computing. or better to say I am confused about what actually
Cloud Computing is. I've seen a lot of articles on this topic. But they were
non technical and I cannot understand it properly.
Is Cloud Computing a replacement of dedicated Server ? If yes then why would I
use it instead of dedicated Server ? What is Pay per use ? The Pricing Plans
looks like VPS Hosting Plan Charts !! If I need a Service (e.g. it might be
some kind of XML service) heavily used by multiple Applications. I'll put Only
the Service in a dedicated server and apps might be hosted in Shared Hosting
(doesn't matter). Wait a min.. Does it mean My Application hosted on a Cloud
will get CDNs like Google, AOL have :( Sorry I am Confused.
I see in Google App Engine I am restricted in Python and Java Only (thats the
reason I was not interested in Google App Engine much from when it released).
and in an article I saw in Amazon there is no persistent storage. Hmmmm What
does it mean ?? Will I've to reupload everything ?? I see I need to start VM
Images there .. So do I need to pay by the time frame when my image was Up ??
But I find no reason to my Apps non-24hrs.
Sorry I am confused. Please Help me to figure it out.
Answer: > Is Cloud Computing a replacement of dedicated Server ?
Sometimes
Depending on the service offered you upload either a virtual machine image
containing all the stuff you want to run, or a single java program. It runs,
you (and your customers) use it.
> If yes then why would I use it instead of dedicated Server ?
You need a database server today - instead of waiting for Dell to deliver it,
then for you to check out the HW, install the OS, configure it, get the
network working, cool it, manage it, secure it - you just click a couple of
buttons on Amazon/Google and your server is running.
Then your service takes off and you need 100 servers tomorrow, or you have a
business model that needs 100 servers on the last day of the month but 1
server all the time. Cloud computing lets you create new servers by the
minute.
> What is Pay per use ?
You pay for how many cores/how many IP addresses/how many machines you use,
for only the time you use them. Unlike buying a machine and OS license for
life.
> Amazon there is no persistent storage.
Amazon also sells storage with their S3 product which you can use either from
your cloud server or your desktop - I suspect their cloud offering uses S3 so
you buy storage separately.
> But I find no reason to my Apps non-24hrs.
You don't have to, most cloud users are using it to drive their website based
business - stackoverflow could (but doesn't) run on the cloud. SO 24x7
availability is important - this is one of the advantages of the cloud, if a
machine dies your image is instantly started on another machine possibly in
another data center.
Others use it for heavy computing jobs and just buy the time on 100s of
machines to complete the calculation then quit them.
|
Indentation Error python
Question: I'm using twisted API and was going through this example. I inserted one print
statement print "in getdummydata" with correct indentation. code is as below:
from twisted.internet import reactor, defer
def getDummyData(x):
"""
This function is a dummy which simulates a delayed result and
returns a Deferred which will fire with that result. Don't try too
hard to understand this.
"""
print "in getdummydata"
d = defer.Deferred()
# simulate a delayed result by asking the reactor to fire the
# Deferred in 2 seconds time with the result x * 3
reactor.callLater(2, d.callback, x * 3)
return d
def printData(d):
"""
Data handling function to be added as a callback: handles the
data by printing the result
"""
print d
d = getDummyData(3)
d.addCallback(printData)
# manually set up the end of the process by asking the reactor to
# stop itself in 4 seconds time
reactor.callLater(4, reactor.stop)
# start up the Twisted reactor (event loop handler) manually
reactor.run()
But when I run the code it gives the indentation error below:
File "C:\Python26\programs\twisttest.py", line 9
print "in getdummydata"
^
IndentationError: unexpected indent
Please can anyone explain why?
Answer: It looks like the "def" for all your functions have one blank space in front
of them. By my eye, "def" falls under the "r" in the "from" above rather than
the "f".
Perhaps if you remove those spaces the problem will go away. Whitespace is
important to Python.
|
Python and OpenMP C Extensions
Question: I have a C extension in which I'd like to use OpenMP. When I import my module,
though, I get an import error:
ImportError: /home/.../_entropysplit.so: undefined symbol: GOMP_parallel_end
I've compiled the module with -fopenmp and -lgomp. Is this because my Python
installation wasn't compiled with the -fopenmp flag? Will I have to build
Python from source? Or is there some other possibility? This is the only time
I actually use openmp in my module:
unsigned int feature_index;
#pragma omp parallel for
for (feature_index = 0; feature_index < num_features; feature_index++) {
I'd like to stick with openmp if it's possible, just because it's so easy and
the parallelization in this case suits it well.
EDIT: I bit the bullet and recompiled Python with OpenMP support. My module
works perfectly now, but this isn't really a great solution. I can't really
distribute this if it requires a complete recompile of Python. So does anybody
know some way around this? Would ctypes work, maybe?
SOLVED! It was a simple linking issue. (I rebuilt Python for that?!) OpenMP
wasn't being properly linked during the compilation of the module. So it _IS_
possible to load a C Python extension that uses OpenMP.
Answer: Just to make it clearer, here is what your setup.py should look like:
ext = Extension(
'milk.unsupervised._som',
sources = ['milk/unsupervised/_som.cpp'],
extra_compile_args=['-fopenmp'],
extra_link_args=['-lgomp'])
...
setup(..., ext_modules = [ext])
|
Trying to parse an XML file with Python - what am I doing wrong?
Question: I'm working with XML and Python for the first time. The ultimate goal is to
send a request to a REST service, receive a response in XML, and parse the
values and send emails depending on what was returned. However, the REST
service is not yet in place, so for now I'm experimenting with an XML file
saved on my C drive.
I have a simple bit of code, and I'm confused about why it isn't working.
This is my xml file ("XMLTest.xml"):
<Response>
<exitCode>1</exitCode>
<fileName>C:/Something/</fileName>
<errors>
<error>Error generating report</error>
</errors>
</Response>
This is my code so far:
from xml.dom import minidom
something = open("C:/XMLTest.xml")
something = minidom.parse(something)
nodeList = []
for node in something.getElementsByTagName("Response"):
nodeList.extend(t.nodeValue for t in node.childNodes)
print nodeList
But the results that print out are...
[u'\n\t', None, u'\n\t', None, u'\n\t', None, u'\n']
What am I doing wrong?
I'm trying to get the node values. Is there a better way to do this? Is there
a built-in method in Python to convert an xml file to an object or dictionary?
I'd like to get all the values, preferably with the names attached.
Answer: Does this help?
doc = '''<Response>
<exitCode>1</exitCode>
<fileName>C:/Something/</fileName>
<errors>
<error>Error generating report</error>
</errors>
</Response>'''
from xml.dom import minidom
something = minidom.parseString( doc )
nodeList = [ ]
for node in something.getElementsByTagName( "Response" ):
response = { }
response[ "exit code" ] = node.getElementsByTagName( "exitCode" )[ 0 ].childNodes[ 0 ].nodeValue
response[ "file name" ] = node.getElementsByTagName( "fileName" )[ 0 ].childNodes[ 0 ].nodeValue
errors = node.getElementsByTagName( "errors" )[ 0 ].getElementsByTagName( "error" )
response[ "errors" ] = [ error.childNodes[ 0 ].nodeValue for error in errors ]
nodeList.append( response )
import pprint
pprint.pprint( nodeList )
yields
[{'errors': [u'Error generating report'],
'exit code': u'1',
'file name': u'C:/Something/'}]
|
Python: virtualenv - gtk-2.0
Question: To add gtk-2.0 to my virtualenv I did the following:
$ virtualenv --no-site-packages --python=/usr/bin/python2.6 myvirtualenv
$ cd myvirtualenv
$ source bin/activate
$ cd lib/python2.6/
$ ln -s /usr/lib/pymodules/python2.6/gtk-2.0/
<http://stackoverflow.com/questions/249283/virtualenv-on-ubuntu-with-no-site-
packages>
Now in the Python interpreter when I do import gtk it says: No module named
gtk. When I start the interpreter with sudo it works.
Any reason why I need to use sudo and is there a way to prevent it?
**Update:**
Forgot to mention that cairo and pygtk work but it's not the one I need.
**Update2:**
Here the directory to show that I ain't crazy. 
Answer: `sudo python` imports it just fine because that interpreter isn't using your
virtual environment. So don't do that.
You only linked in one of the necessary items. Do the others mentioned in the
answer to the question you linked as well.
(The pygtk.pth file is of particular importance, since it tells python to
actually put that directory you linked onto the python path)
## Update
Put that stuff in $VIRTUALENV/lib/python2.6/**site-packages/** rather than the
directory above that.
Looks like the .pth files aren't read from that directory - just from site-
packages
|
error while trying to connect with a cisco 2600 router through python in windows
Question:
The code i have given is
import telnetlib
HOST="X"
user ="X"
password="X"
en_password="x"
tn=telnetlib.Telnet(HOST)
Traceback (most recent call last):
File "<pyshell#15>", line 1, in <module>
tn=telnetlib.Telnet(HOST)
File "C:\Python27\lib\telnetlib.py", line 209, in __init__
self.open(host, port, timeout)
File "C:\Python27\lib\telnetlib.py", line 225, in open
self.sock = socket.create_connection((host, port), timeout)
File "C:\Python27\lib\socket.py", line 567, in create_connection
raise error, msg
error: [Errno 10060] A connection attempt failed because the connected party did not properly respond after a period of time, or established connection failed because connected host has failed to respond
This is the error that i am getting while i am trying to connect to the 2600
router . How to remove this error , and connect to the router through a python
script?
Answer: It's a connection timeout - if you're not having a other networking issues
then it's simply that the router is not accepting connections on the default
telnet port. Are you sure you can connect via port 23? Can you use a telnet
client to connect?
|
wxPython and py2app, CreateActCtx error 0x00000008 (Not enough disk space available)
Question: I've been developing an application that uses wxPython as the GUI librar, and
py2exe so that I can easily distribute it, however I have just now tested
py2exe and the following error appears when the executable is launched.
12:13:08: Debug: src/helpers.cpp(140): 'CreateActCtx' failed with error 0x00000008 (Not enough disk space available.).
Traceback (most recent call last):
File "eYoutubeMacros3.py", line 1, in <module>
File "zipextimporter.pyo", line 82, in load_module
File "application\application.pyo", line 5, in <module>
File "zipextimporter.pyo", line 82, in load_module
File "application\backend\backend.pyo", line 4, in <module>
File "zipextimporter.pyo", line 82, in load_module
File "application\backend\extractor.pyo", line 5, in <module>
File "zipextimporter.pyo", line 82, in load_module
File "twisted\web\client.pyo", line 17, in <module>
File "zipextimporter.pyo", line 82, in load_module
File "twisted\web\error.pyo", line 188, in <module>
ImportError: cannot import name resource
The function causing the error in src/helpers.cpp is
static ULONG_PTR wxPySetActivationContext()
{
OSVERSIONINFO info;
wxZeroMemory(info);
info.dwOSVersionInfoSize = sizeof(OSVERSIONINFO);
GetVersionEx(&info);
if (info.dwMajorVersion < 5)
return 0;
ULONG_PTR cookie = 0;
HANDLE h;
ACTCTX actctx;
TCHAR modulename[MAX_PATH];
GetModuleFileName(wxGetInstance(), modulename, MAX_PATH);
wxZeroMemory(actctx);
actctx.cbSize = sizeof(actctx);
actctx.lpSource = modulename;
actctx.lpResourceName = MAKEINTRESOURCE(2);
actctx.hModule = wxGetInstance();
actctx.dwFlags = ACTCTX_FLAG_HMODULE_VALID | ACTCTX_FLAG_RESOURCE_NAME_VALID;
h = CreateActCtx(&actctx);
if (h == INVALID_HANDLE_VALUE) {
wxLogLastError(wxT("CreateActCtx"));
return 0;
}
if (! ActivateActCtx(h, &cookie))
wxLogLastError(wxT("ActivateActCtx"));
return cookie;
}
And lastly my code for py2exe
setup(
console = [self.target], # Contains some build info, is this is relevant I'll add it
zipfile = 'library.dat',
options = {
'py2exe' : {
'bundle_files' : 1,
'dll_excludes' : ['w9xpopen.exe'],
'optimize' : 2,
'dist_dir' : '../dist/executables/',
'compressed' : True,
#'excludes' : ['doctest', 'pdb', 'unittest', 'difflib', 'inspect'],
}
}
)
Edit: Yes the second error seems to be from twisted but I doubt that causes
the first error. Edit2: Hmm perhaps the first one is just a warning.
Answer: That means common controls stuff does not load. The second error could be a
result of the first error which is non fatal and program continues to run.
try first :
(Don't bundle option) and check if the issue still appears. This should
typically work.
bundle_files = 3
try next:
Since, you are using bundle option 1 , Can you check which MSVC runtime DLL is
located in the dist directory along side the executable. I would suggest that
you also find out all MSVCRXX.dll on your machine and see if there are version
issues
|
Django - make file I/O thread safe
Question: I want to read and write python-source-files from the file system in a thread-
safe way.
open("n2.py","w").write(my_new_py_class)
from myproject import n2
#do something with n2
I assume that this is not thread-safe, since a request2 could modify the file
before request1 is loading and executing it. I would like to achieve something
like that one thread is waiting till the other thread wrote, loaded, executed
and closed the file.
Answer: Why are you making your application modify its own files? This is not only
incredibly evil, metaprogramming is orders of magnitude harder to understand
debug. Plus, python caches modules it imports, so it's not really easy to
reload that. And, last but not least, you don't have to writ the code to a
file to execute it, if you really must execute dynamically generated code.
To answer your question about writing files in a thread safe way, the general
convention is to:
* Write your content to a temporary file on the same filesystem as your target file.
* Rename that temporary file to your target file, overwritting it in the process.
This works, because rename is atomic on POSIX systems, when done on the same
device. So other threads/processes will either still have the old file opened,
which is now detached from the filesystem and will be deleted as soon as those
threads/processes are done with it, or they will open the new file with all of
its contents. You avoid having a file that is only half-written.
In practice, I like to make a temporary directory with python's tempfile
module, and write the file in there, then move it and remove the directory --
this way the file is being created with default umask.
Last but not least, rename is not really atomic on Windows, at least with
default settings, as it won't let you overwrite your old file -- you need to
do two renames, and that introduces a possibility of race condition. I don't
know a good solution for Windows.
|
Any quick Python GUI to display live images from Camera
Question: I am trying to display live images from my 1394 camera. Currently my code is
able to obtain images in a loop from the camera and I was looking for any
quick GUI that will update dynamically (as a separate thread). I can do this
in PyQt maybe using QThreads but is there any recommendation or faster way of
doing this?? Here's my code
#Loop capturing frames from camera
for frame in range(1,500):
print 'frame:',frame
TIME.sleep(1) #capture frame every second
image_binary = pycam.cam.RetrieveBuffer()
#convert to PIL Image
pilimg = PIL.Image.frombuffer("L",(cimg.GetCols(),cimg.GetRows()),image_binary,'raw', "RGBA", 0, 1)
# At this point I want to send my image data to a GUI window and display it
Thank you.
Answer: Here's [wxPython](http://www.wxpython.org/) code that will do it...
import wx
from PIL import Image
SIZE = (640, 480)
def get_image():
# Put your code here to return a PIL image from the camera.
return Image.new('L', SIZE)
def pil_to_wx(image):
width, height = image.size
buffer = image.convert('RGB').tostring()
bitmap = wx.BitmapFromBuffer(width, height, buffer)
return bitmap
class Panel(wx.Panel):
def __init__(self, parent):
super(Panel, self).__init__(parent, -1)
self.SetSize(SIZE)
self.SetBackgroundStyle(wx.BG_STYLE_CUSTOM)
self.Bind(wx.EVT_PAINT, self.on_paint)
self.update()
def update(self):
self.Refresh()
self.Update()
wx.CallLater(15, self.update)
def create_bitmap(self):
image = get_image()
bitmap = pil_to_wx(image)
return bitmap
def on_paint(self, event):
bitmap = self.create_bitmap()
dc = wx.AutoBufferedPaintDC(self)
dc.DrawBitmap(bitmap, 0, 0)
class Frame(wx.Frame):
def __init__(self):
style = wx.DEFAULT_FRAME_STYLE & ~wx.RESIZE_BORDER & ~wx.MAXIMIZE_BOX
super(Frame, self).__init__(None, -1, 'Camera Viewer', style=style)
panel = Panel(self)
self.Fit()
def main():
app = wx.PySimpleApp()
frame = Frame()
frame.Center()
frame.Show()
app.MainLoop()
if __name__ == '__main__':
main()
|
How to make python 3 print() utf8
Question: How to make python 3 (3.1) to print("Some text") to stdout in utf8 ...
or how to output raw bytes..
Test.py
>
> TestText = "Test - āĀēĒčČ..šŠūŪžŽ" # this is UTF-8
> TestText2 = b"Test2 -
> \xc4\x81\xc4\x80\xc4\x93\xc4\x92\xc4\x8d\xc4\x8c..\xc5\xa1\xc5\xa0\xc5\xab\xc5\xaa\xc5\xbe\xc5\xbd"
> # just bytes
> print(sys.getdefaultencoding())
> print(sys.stdout.encoding)
> print(TestText)
> print(TestText.encode("utf8"))
> print(TestText.encode("cp1252","replace"))
> print(TestText2)
>
Output: \\\ in cp1257 and I replaced chars to byte values [xHEX]
> utf-8
> cp1257
> Test - [xE2][xC2][xE7][C7][xE8][xC8]..[xF0][xD0][xFB][xDB][xFE][xDE]
> b'Test -
> \xc4\x81\xc4\x80\xc4\x93\xc4\x92\xc4\x8d\xc4\x8c..\xc5\xa1\xc5\xa0\xc5\xab\xc5\xaa\xc5\xbe\xc5\xbd'
> b'Test - ??????..\x9a\x8a??\x9e\x8e'
> b'Test2 -
> \xc4\x81\xc4\x80\xc4\x93\xc4\x92\xc4\x8d\xc4\x8c..\xc5\xa1\xc5\xa0\xc5\xab\xc5\xaa\xc5\xbe\xc5\xbd'
print() is just too smart... :D
there's no point using encoded text with print (it always show only
representation of bytes not real bytes)
and it's impossible to output bytes at all, because print anyway and always
encodes it in sys.stdout.encoding
for example:
>
> print(chr(255))
>
throws an error
> Traceback (most recent call last):
> File "Test.py", line 1, in
> print(chr(255));
> File "H:\Python31\lib\encodings\cp1257.py", line 19, in encode
> return codecs.charmap_encode(input,self.errors,encoding_table)[0]
> UnicodeEncodeError: 'charmap' codec can't encode character '\xff' in
> position 0: character maps to
by the way print( TestText == TestText2.decode("utf8")); returns False...
although print output is same...
EDIT:
How python 3 gets sys.stdout.encoding and how to change it?
I made printRAW function witch works fine :) (tnx Zack)
(actually it encodes output to UTF-8, so in real it's not raw...)
>
> def printRAW(*Text):
> RAWOut = open(1, 'w', encoding='utf8', closefd=False)
> print(*Text, file=RAWOut)
> RAWOut.flush()
> RAWOut.close()
>
> printRAW("Cool", TestText)
>
output: \\\ now it print in UTF-8
> Cool Test - āĀēĒčČ..šŠūŪžŽ
printRAW(chr(252)) also nicely prints ü (in UTF-8, [xC3][xBC]) and without
errors :)
Now I'm looking for maybe better solution if there's any...
Answer: First, a correction:
TestText = "Test - āĀēĒčČ..šŠūŪžŽ" # this NOT utf-8...it is a Unicode string in Python 3.X.
TestText2 = TestText.encode('utf8') # THIS is "just bytes" in UTF-8.
Now, to send UTF-8 to stdout, regardless of the console's encoding, use the
right tool for the job:
import sys
sys.stdout.buffer.write(TestText2)
"buffer" is a raw interface to stdout.
|
Python: 'Private' module in a package
Question: I have a package `mypack` with modules `mod_a` and `mod_b` in it. I intend the
the package itself and `mod_a` to be imported freely:
import mypack
import mypack.mod_a
However, I'd like to keep `mod_b` for the exclusive use of `mypack`. That's
because it exists merely to organize the latter's internal code.
My first question is, is it an accepted practice in Python programming to have
'private' modules like this?
If yes, my second question is, what is the best way to convey this intention
to the client? Do I prefix the name with an underscore (i.e. `_mod_b`)? Or
would it be a good idea to declare a sub-package `private` and place all such
modules there?
Answer: I prefix private modules with an underscore to communicate the intent to the
user. In your case, this would be `mypack._mod_b`
This is in the same spirit (but not completely analogous to) the PEP8
recommendation to name C-extension modules with a leading underscore when it’s
wrapped by a Python module; i.e., `_socket` and `socket`.
|
Tell pydev to exclude an entire package from analysis?
Question: Today I'm on a mission to remove little red X's from my django project in
pydev. Mostly, this involves fixing import problems with pydev.
I'm using [South](http://south.aeracode.org/) for database migrations. South
(if you don't know) generates python modules, and pydev doesn't like them. I
don't want to edit the south code since it's generated.
Is there a way to instruct pydev to exclude certain packages from analysis?
Something like `#@UndefinedVariable`, except for the entire module? Ideally
I'd like to ignore packages named "migrations".
Answer: In South, I have added a "#@PydevCodeAnalysisIgnore" to the templates in
`south/management/datamigration.py` and `south/management/schemamigration.py`.
It doesn't let me ignore entire packages, but serves my purposes well enough.
|
Creating a simple XML file using python
Question: What are my options if I want to create a simple XML file in python? (library
wise)
The xml I want looks like:
<root>
<doc>
<field1 name="blah">some value1</field1>
<field2 name="asdfasd">some vlaue2</field2>
</doc>
</root>
Answer: These days, the most popular (and very simple) option is the ElementTree API,
which has been included in the standard library since Python 2.5.
The available options for that are:
* ElementTree (Basic, pure-Python implementation of ElementTree. Part of the standard library since 2.5)
* cElementTree (Optimized C implementation of ElementTree. Also offered in the standard library since 2.5)
* LXML (Based on libxml2. Offers a a rich superset of the ElementTree API as well XPath, CSS Selectors, and more)
Here's an example of how to generate your example document using the in-stdlib
cElementTree:
import xml.etree.cElementTree as ET
root = ET.Element("root")
doc = ET.SubElement(root, "doc")
ET.SubElement(doc, "field1", name="blah").text = "some value1"
ET.SubElement(doc, "field2", name="asdfasd").text = "some vlaue2"
tree = ET.ElementTree(root)
tree.write("filename.xml")
I've tested it and it works, but I'm assuming whitespace isn't significant. If
you need "prettyprint" indentation, let me know and I'll look up how to do
that. (It may be an LXML-specific option. I don't use the stdlib
implementation much)
For further reading, here are some useful links:
* [API docs for the implementation in the Python standard library](http://docs.python.org/library/xml.etree.elementtree.html)
* [Introductory Tutorial](http://effbot.org/zone/element-index.htm) (From the original author's site)
* [LXML etree tutorial](http://lxml.de/tutorial.html). (With example code for loading the best available option from all major ElementTree implementations)
As a final note, either cElementTree or LXML should be fast enough for all
your needs (both are optimized C code), but in the event you're in a situation
where you need to squeeze out every last bit of performance, the benchmarks on
the LXML site indicate that:
* LXML clearly wins for serializing (generating) XML
* As a side-effect of implementing proper parent traversal, LXML is a bit slower than cElementTree for parsing.
|
ctypes.windll.user32.GetCursorInfo() - how can I manage this to work? [Python]
Question: I have to get the information about the current mouse cursor from windows but
I'm not managing to work this command...
what should I do? Can someone post one example?
Answer: What information are you trying to get out of the GetCursorInfo() call? It
would be easier to use the [win32
extensions](http://python.net/crew/skippy/win32/Downloads.html) (especially if
you just want cursor position).
>>> import win32gui
>>> win32gui.GetCursorInfo()
(1, 65555, (717, 412))
|
Python matplotlib: memory not being released when specifying figure size
Question: I'm using matplotlib to generate many plots of the results of a numerical
simulation. The plots are used as frames in a video, and so I'm generating
many of them by repeatedly calling a function similar to this one:
from pylab import *
def plot_density(filename,i,t,psi_Na):
figure(figsize=(8,6))
imshow(abs(psi_Na)**2,origin = 'lower')
savefig(filename + '_%04d.png'%i)
clf()
The problem is that the memory usage of the python process grows by a couple
of megabytes with every call to this function. For example if I call it with
this loop:
if __name__ == "__main__":
x = linspace(-6e-6,6e-6,128,endpoint=False)
y = linspace(-6e-6,6e-6,128,endpoint=False)
X,Y = meshgrid(x,y)
k = 1000000
omega = 200
times = linspace(0,100e-3,100,endpoint=False)
for i,t in enumerate(times):
psi_Na = sin(k*X-omega*t)
plot_density('wavefunction',i,t,psi_Na)
print i
then the ram usage grows with time to 600MB. If however I comment out the line
`figure(figsize=(8,6))` in the function definition, then the ram usage stays
steady at 52MB. `(8,6)` is the default figure size and so identical images are
produced in both cases. I'd like to make different sized plots from my
numerical data without running out of ram. How might I force python to free up
this memory?
I've tried `gc.collect()` each loop to force garbage collection, and I've
tried `f = gcf()` to get the current figure and then `del f` to delete it, but
to no avail.
I'm running CPython 2.6.5 on 64 bit Ubuntu 10.04.
Answer: From the docstring for `pylab.figure`:
In [313]: pylab.figure?
> If you are creating many figures, make sure you explicitly call "close" on
> the figures you are not using, because this will enable pylab to properly
> clean up the memory.
So perhaps try:
pylab.close() # closes the current figure
|
Python: How exactly can you take a string, split it, reverse it and join it back together again?
Question: How exactly can you take a string, split it, reverse it and join it back
together again without the brackets, commas, etc. using python?
Answer:
>>> tmp = "a,b,cde"
>>> tmp2 = tmp.split(',')
>>> tmp2.reverse()
>>> "".join(tmp2)
'cdeba'
or simpler:
>>> tmp = "a,b,cde"
>>> ''.join(tmp.split(',')[::-1])
'cdeba'
The important parts here are the [split
function](http://docs.python.org/library/stdtypes.html#str.split) and the
[join function](http://docs.python.org/library/stdtypes.html#str.join). To
reverse the list you can use `reverse()`, which reverses the list in place or
the slicing syntax `[::-1]` which returns a new, reversed list.
|
UDP client and server with Twisted Python
Question: I want to create a server and client that sends and receives UDP packets from
the network using Twisted. I've already written this with sockets in Python,
but want to take advantage of Twisted's callback and threading features.
However, I need help though with the design of Twisted.
I have multiple types of packets I want to receive, but let's pretend there is
just one:
class Packet(object):
def __init__(self, data=None):
self.packet_type = 1
self.payload = ''
self.structure = '!H6s'
if data == None:
return
self.packet_type, self.payload = struct.unpack(self.structure, data)
def pack(self):
return struct.pack(self.structure, self.packet_type, self.payload)
def __str__(self):
return "Type: {0}\nPayload {1}\n\n".format(self.packet_type, self.payload)
I made a protocol class (almost direct copy of the examples), which seems to
work when I send data from another program:
class MyProtocol(DatagramProtocol):
def datagramReceived(self, data, (host, port)):
p = Packet(data)
print p
reactor.listenUDP(3000, MyProtocol())
reactor.run()
What I don't know is how do I create a client which can send arbitrary packets
on the network, which get picked up by the reactor:
# Something like this:
s = Sender()
p = Packet()
p.packet_type = 3
s.send(p.pack())
p.packet_type = 99
s.send(p.pack())
I also need to make sure to set the reuse address flag on the client and
servers so I can run multiple instances of each at the same time on the same
device (e.g. one script is sending heartbeats, another responds to heartbeats,
etc).
Can someone show me how this could be done with Twisted?
**Update** :
This is how I do it with sockets in Python. I can run multiple listeners and
senders at the same time and they all hear each other. How do I get this
result with Twisted? (The listening portion need not be a separate process.)
class Listener(Process):
def __init__(self, ip='127.0.0.1', port=3000):
Process.__init__(self)
self.ip = ip
self.port = port
def run(self):
sock = socket.socket(socket.AF_INET, socket.SOCK_DGRAM)
sock.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1)
sock.bind((self.ip, self.port))
data, from_ip = sock.recvfrom(4096)
p = Packet(data)
print p
class Sender(object):
def __init__(self, ip='127.255.255.255', port=3000):
self.sock = socket.socket(socket.AF_INET, socket.SOCK_DGRAM)
self.sock.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1)
self.ip = (ip, port)
def send(self, data):
self.sock.sendto(data, self.ip)
if __name__ == "__main__":
l = Listener()
l.start()
s = Sender()
p = Packet()
p.packet_type = 4
p.payload = 'jake'
s.send(p.pack())
**Working solution** :
class MySender(DatagramProtocol):
def __init__(self, packet, host='127.255.255.255', port=3000):
self.packet = packet.pack()
self.host = host
self.port = port
def startProtocol(self):
self.transport.write(self.packet, (self.host, self.port))
if __name__ == "__main__":
packet = Packet()
packet.packet_type = 1
packet.payload = 'jake'
s = MySender(packet)
reactor.listenMulticast(3000, MyProtocol(), listenMultiple=True)
reactor.listenMulticast(3000, s, listenMultiple=True)
reactor.callLater(4, reactor.stop)
reactor.run()
Answer: Just like the server example above, there is a client example to. This should
help you get started:
* <http://www.opendocs.net/python/twisted/howto/udp.html>
* <http://twistedmatrix.com/documents/current/core/examples/echoclient_udp.py>
Ok, here is a simple heart beat sender and receiver using datagram protocol.
from twisted.internet.protocol import DatagramProtocol
from twisted.internet import reactor
from twisted.internet.task import LoopingCall
import sys, time
class HeartbeatSender(DatagramProtocol):
def __init__(self, name, host, port):
self.name = name
self.loopObj = None
self.host = host
self.port = port
def startProtocol(self):
# Called when transport is connected
# I am ready to send heart beats
self.loopObj = LoopingCall(self.sendHeartBeat)
self.loopObj.start(2, now=False)
def stopProtocol(self):
"Called after all transport is teared down"
pass
def datagramReceived(self, data, (host, port)):
print "received %r from %s:%d" % (data, host, port)
def sendHeartBeat(self):
self.transport.write(self.name, (self.host, self.port))
class HeartbeatReciever(DatagramProtocol):
def __init__(self):
pass
def startProtocol(self):
"Called when transport is connected"
pass
def stopProtocol(self):
"Called after all transport is teared down"
def datagramReceived(self, data, (host, port)):
now = time.localtime(time.time())
timeStr = str(time.strftime("%y/%m/%d %H:%M:%S",now))
print "received %r from %s:%d at %s" % (data, host, port, timeStr)
heartBeatSenderObj = HeartbeatSender("sender", "127.0.0.1", 8005)
reactor.listenMulticast(8005, HeartbeatReciever(), listenMultiple=True)
reactor.listenMulticast(8005, heartBeatSenderObj, listenMultiple=True)
reactor.run()
The broadcast example simply modifies the above approach:
from twisted.internet.protocol import DatagramProtocol
from twisted.internet import reactor
from twisted.internet.task import LoopingCall
import sys, time
class HeartbeatSender(DatagramProtocol):
def __init__(self, name, host, port):
self.name = name
self.loopObj = None
self.host = host
self.port = port
def startProtocol(self):
# Called when transport is connected
# I am ready to send heart beats
self.transport.joinGroup('224.0.0.1')
self.loopObj = LoopingCall(self.sendHeartBeat)
self.loopObj.start(2, now=False)
def stopProtocol(self):
"Called after all transport is teared down"
pass
def datagramReceived(self, data, (host, port)):
print "received %r from %s:%d" % (data, host, port)
def sendHeartBeat(self):
self.transport.write(self.name, (self.host, self.port))
class HeartbeatReciever(DatagramProtocol):
def __init__(self, name):
self.name = name
def startProtocol(self):
"Called when transport is connected"
self.transport.joinGroup('224.0.0.1')
pass
def stopProtocol(self):
"Called after all transport is teared down"
def datagramReceived(self, data, (host, port)):
now = time.localtime(time.time())
timeStr = str(time.strftime("%y/%m/%d %H:%M:%S",now))
print "%s received %r from %s:%d at %s" % (self.name, data, host, port, timeStr)
heartBeatSenderObj = HeartbeatSender("sender", "224.0.0.1", 8005)
reactor.listenMulticast(8005, HeartbeatReciever("listner1"), listenMultiple=True)
reactor.listenMulticast(8005, HeartbeatReciever("listner2"), listenMultiple=True)
reactor.listenMulticast(8005, heartBeatSenderObj, listenMultiple=True)
reactor.run()
|
Is this a problem with the Django tutorial or a package problem, or is it me?
Question: I'm using Ubuntu 10, python 2.6.5
I'm following this tutorial: <http://www.djangobook.com/en/2.0/chapter02>
I followed all of the steps using cut-and-paste. The following directory
structure was automatically created:
bill@ed-desktop:~/projects$ ls -l mysite
total 36
-rw-r--r-- 1 bill bill 0 2010-09-01 08:18 __init__.py
-rw-r--r-- 1 bill bill 546 2010-09-01 08:18 manage.py
-rw-r--r-- 1 bill bill 20451 2010-09-01 18:50 mysite.wpr
-rw-r--r-- 1 bill bill 3291 2010-09-01 08:18 settings.py
-rw-r--r-- 1 bill bill 127 2010-09-01 11:13 urls.py
-rw-r--r-- 1 bill bill 97 2010-09-01 08:20 views.py
# urls.py
from django.conf.urls.defaults import *
import sys
print sys.path
from mysite.views import hello
urlpatterns = patterns('',
(r'^hello/$', hello),
)
pylint produces this error: Unable to import 'mysite.views'
# views.py
from django.http import HttpResponse
def hello(request):
return HttpResponse("Hello world")
bill@ed-desktop:~/projects/mysite$ python manage.py runserver
Validating models...
0 errors found
Django version 1.2.1, using settings 'mysite.settings'
Development server is running at http://127.0.0.1:8000/
Quit the server with CONTROL-C.
Which resulted in:
Page not found (404)
Request Method: GET
Request URL: http://127.0.0.1:8000/
Using the URLconf defined in mysite.urls, Django tried these URL patterns, in this order:
1. ^hello/$
The current URL, , didn't match any of these.
Why does view.py which is in the main directory contain the following?
from mysite.views import hello
There is no subdirectory 'views'. Although I'm familiar with using packages,
I've never had the need to create my own so I'm a bit confused. I would have
thought that `from views import hello` would be correct.
The step-by-step tutorial looks straight forward and I haven't seen anyone
else come across this problem so I'm a bit perplexed what I've done wrong.
Answer: I'm not sure what your actual question is.
You've requested the root page, `\`, but have only defined a URL for
`\hello\`, so obviously Django can't find what you've requested. If you want
your `hello` view to match against the site root, do this:
urlpatterns = patterns('',
(r'^$', hello),
)
I don't understand the question about the `from mysite.views import hello`.
This will work if the parent of `mysite` is on the Python path.
|
How to write stereo wav files in Python?
Question: The following code writes a simple sine at frequency 400Hz to a mono WAV file.
How should this code be changed in order to produce a **stereo** WAV file. The
second channel should be in a different frequency.
import math
import wave
import struct
freq = 440.0
data_size = 40000
fname = "WaveTest.wav"
frate = 11025.0 # framerate as a float
amp = 64000.0 # multiplier for amplitude
sine_list_x = []
for x in range(data_size):
sine_list_x.append(math.sin(2*math.pi*freq*(x/frate)))
wav_file = wave.open(fname, "w")
nchannels = 1
sampwidth = 2
framerate = int(frate)
nframes = data_size
comptype = "NONE"
compname = "not compressed"
wav_file.setparams((nchannels, sampwidth, framerate, nframes,
comptype, compname))
for s in sine_list_x:
# write the audio frames to file
wav_file.writeframes(struct.pack('h', int(s*amp/2)))
wav_file.close()
Answer: Build a parallel `sine_list_y` list with the other frequency / channel, set
`nchannels=2`, and in the output loop use `for s, t in zip(sine_list_x,
sine_list_y):` as the header clause, and a body with two `writeframes` calls
-- one for `s`, one for `t`. IOW, corresponding frames for the two channels
"alternate" in the file.
See e.g. [this](http://www.sonicspot.com/guide/wavefiles.html) page for a
thorough description of all possible WAV file formats, and I quote:
> Multi-channel digital audio samples are stored as interlaced wave data which
> simply means that the audio samples of a multi-channel (such as stereo and
> surround) wave file are stored by cycling through the audio samples for each
> channel before advancing to the next sample time. This is done so that the
> audio files can be played or streamed before the entire file can be read.
> This is handy when playing a large file from disk (that may not completely
> fit into memory) or streaming a file over the Internet. The values in the
> diagram below would be stored in a Wave file in the order they are listed in
> the Value column (top to bottom).
and the following table clearly shows the channels' samples going left, right,
left, right, ...
|
Alternative to Passing Global Variables Around to Classes and Functions
Question: I'm new to python, and I've been reading that using `global` to pass variables
to other functions is considered noobie, as well as a bad practice. I would
like to move away from using global variables, but I'm not sure what to do
instead.
Right now I have a UI I've created in wxPython as its own separate class, and
I have another class that loads settings from a .ini file. Since the settings
in the UI should match those in the .ini, how do I pass around those values? I
could using something like: `Settings = Settings()` and then define the
variables as something like `self.settings1`, but then I would have to make
`Settings` a global variable to pass it to my UI class (which it wouldn't be
if I assign in it `main()`).
So what is the correct and pythonic way to pass around these variables?
**Edit:** Here is the code that I'm working with, and I'm trying to get it to
work like Alex Martelli's example. The following code is saved in
`Settings.py`:
import ConfigParser
class _Settings():
@property
def enableautodownload(self): return self._enableautodownload
def __init__(self):
self.config = ConfigParser.ConfigParser()
self.config.readfp(open('settings.ini'))
self._enableautodownload=self.config.getboolean('DLSettings', 'enableautodownload')
settings = _Settings()
Whenever I try to refer to `Settings.settings.enableautodownload` from another
file I get: `AttributeError: 'module' object has no attribute 'settings'`.
What am I doing wrong?
**Edit 2:** Never mind about the issue, I retyped the code and it works now,
so it must have been a simple spelling or syntax error.
Answer: The alternatives to `global` variables are many -- mostly:
* explicit arguments to functions, classes called to create one of their instance, etc (this is usually the clearest, since it makes the dependency most explicit, when feasible and not too repetitious);
* instance variables of an object, when the functions that need access to those values are methods on that same object (that's OK too, and a reasonable way to use OOP);
* "accessor functions" that provide the values (or an object which has attributes or properties for the values).
Each of these (esp. the first and third ones) is particularly useful for
values whose names must _not_ be re-bound by all and sundry, but only
accessed. The really big problem with `global` is that it provides a "covert
communication channel" (not in the cryptographic sense, but in the literal
one: apparently separate functions can actually be depending on each other,
influencing each other, via global values that are not "obvious" from the
functions' signatures -- this makes the code hard to test, debug, maintain,
and understand).
For your specific problem, if you never use the `global` statement, but rather
access the settings in a "read-only" way from everywhere (and you can ensure
that more fully by making said object's attributes be read-only properties!),
then having the "read-only" accesses be performed on a single, made-once-then-
not-changed, module-level instance, is not too bad. I.e., in some module
`foo.py`:
class _Settings(object):
@property
def one(self): return self._one
@property
def two(self): return self._two
def __init__(self, one, two):
self._one, self._two = one, two
settings = _Settings(23, 45)
and from everywhere else, `import foo` then just access `foo.settings.one` and
`foo.settings.two` as needed. Note that I've named the class with a single
leading underscore (just like the two instance attributes that underlie the
read-only properties) to suggest that it's not meant to be used from "outside"
the module -- only the `settings` object is supposed to be (there's no
enforcement -- but any user violating such requested privacy is most obviously
the only party responsible for whatever mayhem may ensue;-).
|
ImportError: no module named _jcc
Question: I'm trying to install pylucene on python 2.7 (windows) since four days. It
requires JCC to build and install. After thousands and thousands different
errors I handled myself, at last JCC sucessfully builded and installed. At
least, that was what I thought. After that, I tried to import jcc but I get
this error:
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
File "jcc\__init__.py", line 29, in <module>
from _jcc import initVM
ImportError: No module named _jcc
any ideas? It looks installed perfectly but I can't import it.
Answer: Make sure your current dir is not jcc build directory. I get this error if I
try to import jcc when in build directory, python uses the wrong jcc then.
|
Sql Alchemy > TypeError: 'instancemethod' object does not support item assignment
Question: Here's what I've got:
from sqlalchemy import *
from sqlalchemy.orm import *
from web.models.card import *
connectionString = "postgresql://www:www@localhost/prod"
databaseEngine = create_engine(connectionString)
sessionFactory = sessionmaker(autoflush = True, autocommit = False, bind = databaseEngine)
session = sessionFactory()
CardsCollection = session.query(card).all()
_content = {}
for index in range(0, len(CardsCollection)):
c = CardsCollection[index]
_content[index] = c
print json.dumps(_content)
`
And here's the error:
Traceback (most recent call last):
File "/home/src/py/raspberry/src/dictionaryTest.py", line 15, in
CardsCollection = session.query(card).all()
File "/usr/local/lib/python2.6/dist-packages/sqlalchemy/orm/query.py", line 1453, in all
return list(self)
File "/usr/local/lib/python2.6/dist-packages/sqlalchemy/orm/query.py", line 1676, in instances
rows = [process[0](row, None) for row in fetch]
File "/usr/local/lib/python2.6/dist-packages/sqlalchemy/orm/mapper.py", line 2234, in _instance
populate_state(state, dict_, row, isnew, only_load_props)
File "/usr/local/lib/python2.6/dist-packages/sqlalchemy/orm/mapper.py", line 2113, in populate_state
populator(state, dict_, row)
File "/usr/local/lib/python2.6/dist-packages/sqlalchemy/orm/strategies.py", line 127, in new_execute
dict_[key] = row[col]
TypeError: 'instancemethod' object does not support item assignment
`
Can someone help me out with this? I've tried a few things, and researched
into how dictionaries work... but its just not jumping out at me.
**[edit for strange resolution]** Apparently, overriding the
`self.__dict__(self)` method on the card model is what did it. I'm not
entirely sure why, though.
Answer: `__dict__` is a [special
attribute](http://docs.python.org/reference/datamodel.html#index-862) holding
current state of instance, overwriting it with with method will certainly lead
to troubles.
|
How to create a simple mesh in Blender 2.50 via the Python API
Question: I would like to create a simple mesh in Blender (2.50) via the Python API but
the examples from the API documentation don't work yet.
I tried the following but it's [from API
2.49](http://www.blender.org/documentation/249PythonDoc/Mesh-module.html)
from Blender import *
import bpy
editmode = Window.EditMode() # are we in edit mode? If so ...
if editmode: Window.EditMode(0) # leave edit mode before getting the mesh
# define vertices and faces for a pyramid
coords=[ [-1,-1,-1], [1,-1,-1], [1,1,-1], [-1,1,-1], [0,0,1] ]
faces= [ [3,2,1,0], [0,1,4], [1,2,4], [2,3,4], [3,0,4] ]
me = bpy.data.meshes.new('myMesh') # create a new mesh
me.verts.extend(coords) # add vertices to mesh
me.faces.extend(faces) # add faces to the mesh (also adds edges)
me.vertexColors = 1 # enable vertex colors
me.faces[1].col[0].r = 255 # make each vertex a different color
me.faces[1].col[1].g = 255
me.faces[1].col[2].b = 255
scn = bpy.data.scenes.active # link object to current scene
ob = scn.objects.new(me, 'myObj')
if editmode: Window.EditMode(1) # optional, just being nice
This does not work because the mesh object doesn't have any `faces` or `verts`
members.
Are there any options to do this?
Answer: Try [this](http://www.blender.org/documentation/250PythonDoc/) documentation
for the 2.5x API. I understand that despite the big warnings at the top, the
most used sections are fairly stable now. I've not tried it yet.
EDIT:
I think the relevant bit is [this
section](http://www.blender.org/documentation/blender_python_api_2_72_release/bpy.types.Mesh.html#bpy.types.Mesh.from_pydata)
\- it seems you create a list of vertices faces etc. and pass it to this. This
seems to have changed from the most recent examples I can find. Try looking in
your scripts folder - there might be an example there that you can look at.
EDIT 2: I have updated the link to point to the current live docs. The notes
there suggest that there are probably better ways of doing this now but it is
a long time since I have done any blender scripting so can't help more.
|
Problem decrypting PGP in python with pyme without user interaction
Question: I am trying to decrypt messages using pyme (a python wrapper from gpgme). It
works fine if I type in the password when it prompts but I cannot get the
passphrase callback to work. Here is the code
import pyme.core
def Callback( x, y, z ):
print 'in passphrase callback'
return 'passphrase'
plain = pyme.core.Data()
cipher = pyme.core.Data(sys.stdin.read())
c = pyme.core.Context()
c.set_armor(1)
c.set_passphrase_cb(Callback)
c.op_decrypt( cipher, plain )
plain.seek(0,0)
print plain.read()
When I run this and don't provide the password interactively the program then
tries the Callback printing 'in passphrase callback' but then fails with
error:
pyme.errors.GPGMEError: Invocation of gpgme_op_decrypt: Unspecified source: General error (0,1)
First and foremost, why does the passphrase callback not work? And secondly,
how can I prevent the program from prompting the user for a password before
calling the passphrase callback?
This is running on Ubuntu 10.04
Answer: apparently, you need to interpret the keyword `hook`:
def Callback( x, y, z, hook=None):
...
works perfectly well.
|
how to shift a datetime object by 12 hours in python
Question: Datetime objects hurt my head for some reason. I am writing to figure out how
to shift a date time object by 12 hours. I also need to know how to figure out
if two date time object's differ by say 1 minute or more.
Answer: The [`datetime`](http://docs.python.org/library/datetime.html) library has a
`timedelta` object specifically for this kind of thing:
import datetime
mydatetime = datetime.now() # or whatever value you want
twelvelater = mydatetime + datetime.timedelta(hours=12)
twelveearlier = mydatetime - datetime.timedelta(hours=12)
difference = abs(some_datetime_A - some_datetime_B)
# difference is now a timedelta object
# there are a couple of ways to do this comparision:
if difference > timedelta(minutes=1):
print "Timestamps were more than a minute apart"
# or:
if difference.total_seconds() > 60:
print "Timestamps were more than a minute apart"
|
Python: why does my list change after I've retrieved it from an object
Question:
Simple question, I've scaled down a problem I'm having where a list which I've
retrieve from an object is changing when I append more data to the object. Not
to the list.
Can anyone help my understand the behavior of python?
class a():
def __init__(self):
self.log = []
def clearLog(self):
del self.log[:]
def appendLog(self, info):
self.log.append(str(info))
def getLog(self):
return self.log
if __name__ == '__main__':
obj = a()
obj.appendLog("Hello")
# get an instance as of this moment....
list = obj.getLog()
print list
obj.appendLog("World")
# print list, BUT we want the instance that was obtained
# before the new appendage.
print list
**OutPut:**
['Hello']
['Hello', 'World']
Answer: When you code
`list = obj.getLog()`
(ignoring -- just for a second -- what a **terrible** idea it is to use
identifiers that shadow builtins!!!) you're saying: "make name `list` refer to
exactly the same object that `obj.getLog()` returns" -- which as we know from
the code for `class a` is `obj.log`. So of course since now you have one list
object with two names, when you alter that object through **either** name, all
alterations will be fully visible from both names, of course -- remember,
there _is_ just **one** object, you're just using multiple names for it! You
never asked for a copy, so of course Python made no copies.
When you want a copy, instead of the original, **ask for one**! When you know
the type you require (here, a list), the best way is to call the type, i.e.:
mylist = list(obj.getLog())
This of course becomes impossible if you choose to trample all over the
builtins with your identifiers -- -- which is a good part of why such
identifier choice is a **BAD** idea (I can't stress that enough: it's hard to
think of any worse style choice, to use in your Python coding, than such
naming). So, I've renamed the identifier to `mylist` (and of course you need
to rename it in the two `print` statements).
You **could** use highly unreadable or slower approaches to make up for the
wanton destruction of the normal functionality of built-in identifier `list`,
of course -- e.g.:
import copy
list = copy.copy(obj.getLog()) # somewhat slower
or
list = obj.getLog()[:] # traditional, but ECCH
or
temp = obj.getLog()
list = type(temp)(temp) # abstruse
but **BY FAR** the simplest, cleanest, most recommended approach is to **NOT**
name your identifiers the same as Python built-ins (it's also a nice idea to
avoid naming them just like modules in the standard Python library, for
similar though a bit weaker reasons).
|
How to integrate Sikuli scripts into Selenium?
Question: I'm extensively using [Selenium](http://seleniumhq.org/) for integration
testing. Works great for all normal stuff (HTML/AJAX), but no go when I'm
trying to test third party ActiveX, Java applets and Flash components.
The solution I've found for this is
[Sikuli](http://groups.csail.mit.edu/uid/sikuli/). Works great locally, but
how can I integrate that into Selenium?
btw. if that's relevant, for Selenium I'm using Python API.
Answer: See the Python section of the Selenium RC documentation:
<http://seleniumhq.org/docs/05_selenium_rc.html#python>
You may be able to run Selenium tests from Jython. In that case, you can
simply integrate Selenium scripts into your Sikuli scripts.
Try the following in the Sikuli IDE. You may need to modify the import
statements to point to specific files in the Selenium project.
from selenium import selenium # this will probably need tweaking...
slm = selenium("localhost", 4444, "*firefox", "http://www.google.com/")
slm.start()
# etc...
This guy appears to have had success controlling Selenium from Jython:
<http://adam.goucher.ca/?p=367>
My conclusion: it will probably be easiest to stay in Jython and control
Selenium from there. You could integrate both tools into a single script.
|
How to manipulate the response object in django-piston?
Question: I have some existing python code that uses django-piston which returns a
dictionary as its response. For example:
from piston.handler import BaseHandler
class FooHandler(BaseHandler):
allowed_methods = ('GET',)
@classmethod
def create(self, request):
return { 'foo': 'bar' }
This code works fine, and is serialized into JSON with the appropriate HTTP
header set (I'm assuming this works by some piston magic involving emitters;
for bonus points, feel free to clarify how this behavior works as well, as I'm
still getting to know django-piston).
I need to be able to modify the response in arbitrary ways, e.g. setting
headers, status codes, etc. without using some pre-baked solution designed for
a specific purpose. Is there a convenient way to access the response object in
the context of this code and manipulate it, or has the response object not yet
been created? In order to get access to a response object, will I have to
construct it manually (a la vanilla django), serialize the dictionary, and set
the appropriate headers by hand, and thus lose out on some of the useful magic
of django-piston?
Answer: Every django-piston method returns an HTTPResponse.
When you return that dictionary, django-piston is just serializing it and
sticking it in an HTTPResponse that it has crafted of some variety.
Kind of surprised you didn't pick up on that given that those "return
rc.CREATED" lines in all the django-piston examples in the wiki are just
hyper-simplistic responses with an HTTP code and response body.
Take a look here: <https://bitbucket.org/jespern/django-
piston/src/c4b2d21db51a/piston/utils.py>
at the rc_factory class, which creates a variety of simple HTTPResponse
objects for use with Piston.
At the very least you can observe how they do it, and then craft your own.
But the answer to the essence of your question "can I make a custom
HTTPResponse" is yes, you can. Of course, that's what web servers _do_.
|
How would I go about downloading a file from a submitted link then reuploading to my server for streaming?
Question: I'm working on a project where a user can submit a link to a sound file hosted
on another site through a form. I'd like to download that file to my server
and make it available for streaming. I might have to upload it to Amazon S3.
I'm doing this in Django but I'm new to Python. Can anyone point me in the
right direction for how to do this?
Answer: Here's how I would do it:
1. Create a model like `SoundUpload` like:
class SoundUpload(models.Model):
STATUS_CHOICES = (
(0, 'Unprocessed'),
(1, 'Ready'),
(2, 'Bad File'),
)
uploaded_by = models.ForeignKey(User)
original_url = models.URLField(verify_true=False)
download_url = models.URLField(null=True, blank=True)
status = models.IntegerField(choices=STATUS_CHOICES, default=0)
2. Next create the view w/a `ModelForm` and save the info to the database.
3. Hook up a [post-save signal](http://docs.djangoproject.com/en/dev/ref/signals/#django.db.models.signals.post_save) on the `SoundUpload` model that kicks of a [django-celery](http://pypi.python.org/pypi/django-celery) [Task](http://ask.github.com/celery/userguide/tasks.html). This will ensure that the UI responds while you're processing all the data.
def process_new_sound_upload(sender, **kwargs):
# Bury to prevent circular dependency issues.
from your_project.tasks import ProcessSoundUploadTask
if kwargs.get('created', False):
instance = kwargs.get('instance')
ProcessSoundUploadTask.delay(instance.id)
post_save.connect(process_new_sound_upload, sender=SoundUpload)
4. In the `ProcessSoundUploadTask` task you'll want to:
* Lookup the model object based on the passed in id.
* Using [`pycurl`](http://pycurl.sourceforge.net/) download the file to a temporary folder (w/very limitied permissions).
* Use [`ffmpeg`](http://ffmpeg.org/) (or similar) to ensure it's a real sound file. Do any other virus style checks here (depends on how much you trust your users). If it turn out to be a bad file set the `SoundUpload`.status field to `2` (Bad File), save it, and return to stop processing the task. Perhaps send out an email here.
* Use [`boto`](http://code.google.com/p/boto/) to upload the file to s3. See [this](http://ferrouswheel.me/2009/12/upload-a-file-to-s3-with-boto/) example.
* Update the `SoundUpload`.download_url to be the s3 url, the status to be "processed" and save the object.
* Do any other post-processing (sending notification emails, etc.)
The key to this approach is using `django-celery`. Once the task is kicked off
through the post_save signal the UI can return, thus creating a very "snappy"
experience. This task gets put onto an
[AMQP](http://www.amqp.org/confluence/display/AMQP/Advanced+Message+Queuing+Protocol)
message queue that can be processed by multiple workers (dedicated EC2
instances, etc.), so you'll be able to scale without too much trouble. This
may seem like a bit overkill, but it's really not as much work as it seems.
|
Run custom Django management command over SSH
Question: I have a Django application with a custom management command in one of the
apps. If I log in over SSH I can run it without any problems with
> python manage.py sitedir/mycommand
However, if I try to run the command as a oneliner from my local box like
this:
> ssh myserver python manage.py sitedir/mycommand
I get an ImportError like this:
Traceback (most recent call last):
File "mysite/manage.py", line 11, in <module>
execute_manager(settings)
File "/usr/lib/python2.5/site-packages/django/core/management/__init__.py", line 438, in execute_manager
utility.execute()
File "/usr/lib/python2.5/site-packages/django/core/management/__init__.py", line 379, in execute
self.fetch_command(subcommand).run_from_argv(self.argv)
File "/usr/lib/python2.5/site-packages/django/core/management/__init__.py", line 261, in fetch_command
klass = load_command_class(app_name, subcommand)
File "/usr/lib/python2.5/site-packages/django/core/management/__init__.py", line 67, in load_command_class
module = import_module('%s.management.commands.%s' % (app_name, name))
File "/usr/lib/python2.5/site-packages/django/utils/importlib.py", line 35, in import_module
__import__(name)
ImportError: No module named mysite.myapp.management.commands.mycommand
The real reason is that I want to run this admin command from a Fabric script
but until I can get it to run via the ssh one-liner I guess it will be
impossible. Is there something in the environment that differs when you run it
via the ssh one-liner? The python path seems correct in both cases.
Answer: I think I have a clue what is going on. I don't know how to fix it yet.
To reproduce your scenario I wrote a small script.
#!/usr/bin/python
import sys, django
print django.VERSION
After which I executed it after logging in through SSH as well as remotely
(`ssh yourserver.com "python /home/me/script.py"`) and everything went fine.
Then I changed the script.
#!/usr/bin/python
import os
print os.environ['DJANGO_SETTINGS_MODULE']
This version worked when I logged in to the server but **failed** when I tried
to execute it remotely.
Traceback (most recent call last):
File "/home/me/script.py", line 3, in <module>
print os.environ['DJANGO_SETTINGS_MODULE']
File "/usr/lib/python2.5/UserDict.py", line 22, in __getitem__
raise KeyError(key)
KeyError: 'DJANGO_SETTINGS_MODULE'
Apparently the `DJANGO_SETTINGS_MODULE` environment variable is not set when
you execute the command remotely over SSH. I suspect this _**may**_ be what is
going wrong in your case. You will need to figure out how to make sure that
this variable is properly set before executing the script.
~~Perhaps you can explicitly set it:`os.environ['DJANGO_SETTINGS_MODULE'] =
'foo'`.~~.
Try this:
ssh yourserver.com "python /home/me/script.py" -t
DJANGO_SETTINGS_MODULE=app.settings.custom
|
Why is the Python script unreliable when run from rc.local on first boot?
Question: The script below works great when logged in as root and run from the command
line, but when run at first boot using /etc/rc.local in Ubuntu 10.04, it fails
about 25% of the time- the system root, mysql root and some mysql user
passwords are set correctly, but one will fail with console log reporting
standard mysql login error: "ERROR 1045 (28000): Access denied for user 'root'
@ 'localhost' (using password: YES)"
Is there something about running python scripts from init jobs that I should
account for, such as an environment variable?
#!/usr/bin/env python
# Randomizes and outputs to files the system root and mysql user passwords
files = ['/home/ubuntu/passwords','/opt/data1/alfresco/extensions/
extension/alfresco-global.properties','/opt/data/etc/mysql/
debian.cnf','/home/ubuntu/duncil']
userpasswords = {'root':'ROOTPASSWORD'}
mysqlpasswords =
{'root':'MYSQLPASSWORD','alfresco':'alfrescoPASSWORD','debian-sys-
maint':'debian-sys-maintPASSWORD'}
otherpasswords = ['OTHERPASSWORD']
log = '/var/log/firstrun'
import random, string
import crypt
import re
from subprocess import PIPE, Popen
def getsalt(chars = string.letters + string.digits):
# generate a random 2-character 'salt'
return random.choice(chars) + random.choice(chars)
def getpwd(chars = string.letters + string.digits, len = 12):
retval = "";
for i in range(0, len):
# generate 12 character alphanumeric password
retval += random.choice(chars)
return retval
def replace_pass(filename):
handle = open(filename, 'r')
hbuf = handle.read()
handle.close()
for placeholder, password in pdict.iteritems():
hbuf = re.sub(placeholder, password, hbuf)
try:
# Output file
handle = open(filename, 'w')
handle.write(hbuf)
handle.close()
except:
pass
#logh.write('failed to update ' + filename + "\n")
#logh.write('maybe you don\'t have permision to write to it?\n')
logh = open(log, "a")
logh.write("Starting...\n")
# Generate passwords
pdict = {}
for user, placeholder in userpasswords.iteritems():
syspass = getpwd()
Popen(['usermod', '--password', crypt.crypt(syspass, getsalt()), user])
logh.write(placeholder + ": User " + user + " --> " + syspass + "\n")
pdict[placeholder] = syspass
# Whats the MySQL Root password placeholder?
mplace = mysqlpasswords['root']
for user, placeholder in mysqlpasswords.iteritems():
mpass = getpwd()
if (("root" in mysqlpasswords) and (mysqlpasswords['root'] in pdict)):
mrootpass = pdict[mysqlpasswords['root']]
else:
mrootpass = ""
Popen(['mysql', '-uroot', "--password=" + mrootpass, "-e", "UPDATE user SET Password = PASSWORD('" + mpass + "') WHERE User = '" + user + "';FLUSH PRIVILEGES;","mysql"])
logh.write(placeholder + ": MySQL " + user + " --> " + mpass + "\n")
pdict[placeholder] = mpass
for placeholder in otherpasswords:
opass = getpwd()
logh.write(placeholder + ": " + opass + "\n")
pdict[placeholder] = opass
# Update passwords
for file in files:
logh.write("Replacing placeholders in " + file + "\n")
replace_pass(file)
logh.write("Finished\n")
logh.close
Answer: Doesn't `Popen` execute asynchronously?
It seems that during boot, the load is high and you are getting a race
condition between setting the root password and using it to set the next
password (next command).
Try
p = Popen(['mysql', '-uroot', "--password=" + mrootpass, "-e", "UPDATE user SET Password = PASSWORD('" + mpass + "') WHERE User = '" + user + "';FLUSH PRIVILEGES;","mysql"])
p.wait()
and see if that does it.
|
Python bizarre class problem
Question: I have the following piece of code where I try to override a method:
import Queue
class PriorityQueue(Queue.PriorityQueue):
def put(self, item):
super(PriorityQueue, self).put((item.priority, item))
However, when I run it I get `TypeError` exception:
super() argument 1 must be type, not classobj
What is the problem?
Answer: `Queue.PriorityQueue` is not a new-style class, and `super` [only works with
new-style classes](http://docs.python.org/library/functions.html#super). You
must use
import Queue
class PriorityQueue(Queue.PriorityQueue):
def put(self, item):
Queue.PriorityQueue.put(self,(item.priority, item))
instead.
|
How do I add basic authentication to a Python REST request?
Question: I have the following simple Python code that makes a simple post request to a
REST service -
params= { "param1" : param1,
"param2" : param2,
"param3" : param3 }
xmlResults = urllib.urlopen(MY_APP_PATH, urllib.urlencode(params)).read()
results = MyResponseParser.parse(xmlResults)
The problem is that the url used to call the REST service will now require
basic authentication (username and password). How can I incorporate a username
and password / basic authentication into this code, as simply as possible?
Answer: If basic authentication = HTTP authentication, use this:
import urllib
import urllib2
username = 'foo'
password = 'bar'
passman = urllib2.HTTPPasswordMgrWithDefaultRealm()
passman.add_password(None, MY_APP_PATH, username, password)
authhandler = urllib2.HTTPBasicAuthHandler(passman)
opener = urllib2.build_opener(authhandler)
urllib2.install_opener(opener)
params= { "param1" : param1,
"param2" : param2,
"param3" : param3 }
xmlResults = urllib2.urlopen(MY_APP_PATH, urllib.urlencode(params)).read()
results = MyResponseParser.parse(xmlResults)
If not, use `mechanize` or `cookielib` to make an additional request for
logging in. But if the service you access has an XML API, this API surely
includes auth too.
**2016 edit:** By all means, use the [requests](http://docs.python-
requests.org/en/latest/) library! It provides all of the above in a single
call.
|
IronPython, importing Modules
Question: I follow the example from the best answer here to a T, compiling with Pyc.py.
<http://stackoverflow.com/questions/2139202/build-python-scripts-and-call-
methods-from-c>
I get an exception at `pyScope = pyEngine.ImportModule("MyClass");`
no module named MyClass
I believe this to be a bug as sometimes recompilation with Pyc.py will produce
a dll ImportModule recognizes, but other times it doesn't.
CONCLUSION: As noted below by digEmAll, compiling modules with Pyc.py to be
used in this fashion produces random results. Call clr.CompileModules manually
instead.
Answer: OK, I got it.
The module name is the (case sensitive) name of the original .py module, not
the compiled dll.
I mean, if your original module name was `myClass.py`, then you compiled it in
`MyClass.dll`, you must `ImportModule("myClass")` not
`ImportModule("MyClass")`
* * *
**EDIT:**
the previous code refers to the following compile method:
import clr
clr.CompileModules("CompiledScript.dll", "script.py")
On the contrary, using `pyc.py`, the generated dll contains a module called
`__main__` instead of the `.py` file name.
That's very strange...
IIRC, in python a module call itself `__main__` if it's running standalone
(i.e. not called by another), but I still don't grasp the connection...
|
How to clear cookies in WebKit?
Question: i'm currently working with PyWebKitGtk in python
(http://live.gnome.org/PyWebKitGtk). I would like to clear all cookies in my
own little browser. I found interesting method
webkit.HTTPResponse.clearCookies() but I have no idea how to lay my hands on
instance of HTTPResponse object :/
I wouldn't like to use java script for that task.
Answer: If you look at the current state of the bindings on
[GitHub](https://github.com/jmalonzo/pywebkitgtk/), you'll see PyWebKitGTK
[doesn't yet
provide](https://github.com/jmalonzo/pywebkitgtk/blob/master/webkit/webkit-1.1-types.defs)
quite what you want- there's not mapping for the `HTTPResponse` type it looks
like. Unfortunately, I think Javascript or a proxy are your only options right
now.
EDIT:
...unless, of course, you want it _real_ bad and stay up into the night
learning ctypes. In which case, you can do magic. To clear _all_ the browser's
cookies, try this.
import gtk, webkit, ctypes
libwebkit = ctypes.CDLL('libwebkit-1.0.so')
libgobject = ctypes.CDLL('libgobject-2.0.so')
libsoup = ctypes.CDLL('libsoup-2.4.so')
v = webkit.WebView()
#do whatever it is you do with WebView...
....
#get the cookiejar from the default session
#(assumes one session and one cookiesjar)
generic_cookiejar_type = libgobject.g_type_from_name('SoupCookieJar')
cookiejar = libsoup.soup_session_get_feature(session, generic_cookiejar_type)
#build a callback to delete cookies
DEL_COOKIE_FUNC = ctypes.CFUNCTYPE(None, ctypes.c_void_p)
def del_cookie(cookie):
libsoup.soup_cookie_jar_delete_cookie(cookiejar, cookie)
#run the callback on all the cookies
cookie_list = libsoup.soup_cookie_jar_all_cookies(cookiejar)
libsoup.g_slist_foreach(cookie_list, DEL_COOKIE_FUNC(del_cookie), None)
EDIT:
Just started needing this myself, and while it's the right idea it needed
work. Instead, try this- the function type and cookiejar access are fixed.
#add a new cookie jar
cookiejar = libsoup.soup_cookie_jar_new()
#uncomment the below line for a persistent jar instead
#cookiejar = libsoup.soup_cookie_jar_text_new('/path/to/your/cookies.txt',False)
libsoup.soup_session_add_feature(session, cookiejar)
#build a callback to delete cookies
DEL_COOKIE_FUNC = ctypes.CFUNCTYPE(ctypes.c_int, ctypes.c_void_p, ctypes.c_void_p)
def del_cookie(cookie, userdata):
libsoup.soup_cookie_jar_delete_cookie(cookiejar, cookie)
return 0
#run the callback on all the cookies
cookie_list = libsoup.soup_cookie_jar_all_cookies(cookiejar)
libsoup.g_slist_foreach(cookie_list, DEL_COOKIE_FUNC(del_cookie), None)
Note that you should only do this _before_ using the WebView, or maybe in
WebKit callbacks, or you will have threading issues above and beyond those
usually associated with GTK programming.
|
py2exe problems
Question:
c:\python26\setup.py py2exe
Trying to run py2exe and when I get to command prompt I run the line above.
However as opposed to converting my file it try's to open it. What am I doing
wrong?
Answer: You must create your own `setup.py` and then run it with py2exe:
c:\my_python_scripts>python setup.py py2exe
In your `setup.py` you import `distutils`, `py2exe` and show names of your
scripts to compile. There is template for it. Then I usually create `.bat`
file which compiles my scripts.
Have you read [py2exe tutorial](http://www.py2exe.org/index.cgi/Tutorial)?
|
Propagating Clips Error Messages in PyClips
Question: I'm finding it very difficult to develop with PyClips, because it appears to
replace useful error messages thrown by Clips with a generic "syntax error"
message. This makes debugging very laborious and practically impossible on
large codebases when using PyClips.
Consider the following example. I wrote a very large expression, which
contained the multiplication operator, but I mistakenly forgot to add the
second argument. Instead of simply telling I was missing an argument, PyClips
told me there was a syntax error. What should have taken me 1 second to
correct, took me 5 minutes to correct as I hunted through my large expression,
looking for the mistake.
Here's a condensed version:
In Clips, with a useful error message:
clips
CLIPS> (defrule myrule "" (myfact 123) => (bind ?prob (* (min 1 2))))
[ARGACCES4] Function * expected at least 2 argument(s)
ERROR:
(defrule MAIN::myrule ""
(myfact 123)
=>
(bind ?prob (* (min 1 2))
And in PyClips, with an unuseful error message:
python
>>> import clips
>>> clips.BuildRule('myrule','(myfact 123)','(bind ?prob (* (min 1 2)))','')
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
File "/usr/local/lib/python2.6/dist-packages/clips/_clips_wrap.py", line 2839, in BuildRule
_c.build(construct)
_clips.ClipsError: C08: syntax error, or unable to parse expression
How can I get PyClips to give me the _real_ error thrown by Clips?
Answer: Catch the ClipsError, then read ErrorStream for the details. For example:
engine = clips.Environment()
engine.Reset()
engine.Clear()
try:
engine.Load(os.path.abspath(rule_file))
except clips.ClipsError:
logging.error(clips.ErrorStream.Read())
|
python 2.6.x theading / signals /atexit fail on some versions?
Question: I've seen a lot of questions related to this... but my code _works_ on python
2.6.2 and _fails_ to work on python 2.6.5. Am I wrong in thinking that the
whole atexit "functions registered via this module are not called when the
program is killed by a signal" thing shouldn't count here because I'm catching
the signal and then exiting cleanly? What's going on here? Whats the proper
way to do this?
import atexit, sys, signal, time, threading
terminate = False
threads = []
def test_loop():
while True:
if terminate:
print('stopping thread')
break
else:
print('looping')
time.sleep(1)
@atexit.register
def shutdown():
global terminate
print('shutdown detected')
terminate = True
for thread in threads:
thread.join()
def close_handler(signum, frame):
print('caught signal')
sys.exit(0)
def run():
global threads
thread = threading.Thread(target=test_loop)
thread.start()
threads.append(thread)
while True:
time.sleep(2)
print('main')
signal.signal(signal.SIGINT, close_handler)
if __name__ == "__main__":
run()
python 2.6.2:
$ python halp.py
looping
looping
looping
main
looping
main
looping
looping
looping
main
looping
^Ccaught signal
shutdown detected
stopping thread
python 2.6.5:
$ python halp.py
looping
looping
looping
main
looping
looping
main
looping
looping
main
^Ccaught signal
looping
looping
looping
looping
...
looping
looping
Killed <- kill -9 process at this point
The main thread on 2.6.5 appears to never execute the atexit functions.
Answer: The root difference here is actually unrelated to both signals and atexit, but
rather a change in the behavior of `sys.exit`.
Before around 2.6.5, `sys.exit` (more accurately, SystemExit being caught at
the top level) would cause the interpreter to exit; if threads were still
running, they'd be terminated, just as with POSIX threads.
Around 2.6.5, the behavior changed: the effect of `sys.exit` is now
essentially the same as returning from the main function of the program. When
you do _that_ \--in both versions--the interpreter waits for all threads to be
joined before exiting.
The relevant change is that `Py_Finalize` now calls
`wait_for_thread_shutdown()` near the top, where it didn't before.
This behavioral change seems incorrect, primarily because it no longer
functions as documented, which is simply: "Exit from Python." The practical
effect is no longer to exit from Python, but simply to exit the thread. (As a
side note, `sys.exit` has never exited Python when called from another thread,
but that obscure divergance from documented behavior doesn't justify a much
bigger one.)
I can see the appeal of the new behavior: rather than two ways to exit the
main thread ("exit and wait for threads" and "exit immediately"), there's only
one, as sys.exit is essentially identical to simply returning from the top
function. However, it's a breaking change and diverges from documented
behavior, which far outweighs that.
Because of this change, after `sys.exit` from the signal handler above, the
interpreter sits around waiting for threads to exit and then runs `atexit`
handlers after they do. Since it's the handler itself that tells the threads
to exit, the result is a deadlock.
|
Python set error reporting level like in PHP
Question: How can I set error reporting and warning outputs in Python like in PHP
`error_reporting(E_LEVEL)`?
Answer: A vaguely related option might be the setting of level in the
[`logging`](http://docs.python.org/library/logging.html) module of the Python
standard library, and I quote from Python's docs:
import logging
LOG_FILENAME = 'example.log'
logging.basicConfig(filename=LOG_FILENAME,level=logging.DEBUG)
logging.debug('This message should go to the log file')
That `level=` determines which logging messages are emitted and which ones are
filtered. However this only applies to errors (and other messages) emitted
through `logging` module functions, **not** to (e.g) tracebacks resulting from
exceptions; if you want to control the latter (what kinds of message come out
when the process dies by propagating an exception), you can build something
based on
[sys.excepthook](http://docs.python.org/library/sys.html#sys.excepthook), but
your degrees of freedom will still be somewhat limited (in particular, after
the reporting -- abundant or scarce as it may be -- the process _will_ exit if
an exception has propagated to that point).
|
Efficient way to store dictionary (hash) in file with python?
Question: I'm implementing a Unix userland tool that needs to store a hash on the disk.
The hash will be read every run of the program, pretty frequently. The hash
needs to store "name:path" values only.
I looked at the [bsddb](https://docs.python.org/2/library/bsddb.html) standard
library module for python, but I can see it will be deprecated in Python 3. I
also saw the [pickle](https://docs.python.org/3/library/pickle.html) standard
library module.
I'm not a python guy, so what is the efficient way for hash serialization and
frequent open/read/close operations?
Answer: I would start with the [shelve](http://docs.python.org/library/shelve.html)
module and see if that isn't too slow. It does exactly what you want.
import shelve
d = shelve.open('filename')
d['name'] = 'path'
d.close()
or to read from it
d = shelve.open('filename')
d = hash['name']
It's essentially a wrapper around pickle that provides a dictionary
abstraction.
|
Python ssl problem with multiprocessing
Question: I want to send data from a client to the server in a TLS TCP socket from
multiple client subprocesses so I share the same ssl socket with all
subprocesses. Communication works with one subprocess, but if I use more than
one subprocesses, the TLS server crashes with an `ssl.SSLError`
(SSL3_GET_RECORD:decryption failed or bad record mac).
**More specific:** It does not depend which process first calls the
`SSLSocket.write()` method, but this process is the only one from this time on
which can call it. If another process calls `write()`, the server will result
in the exception described above.
I used this basic code:
**tlsserver.py**
import socket, ssl
def deal_with_client(connstream):
data = connstream.read()
while data:
print data
data = connstream.read()
connstream.close()
bindsocket = socket.socket()
bindsocket.bind(('127.0.0.1', 9998))
bindsocket.listen(5)
while True:
newsocket, fromaddr = bindsocket.accept()
connstream = ssl.wrap_socket(newsocket,
server_side=True,
certfile="srv.crt",
keyfile="srv.key",
ssl_version=ssl.PROTOCOL_TLSv1)
deal_with_client(connstream)
**tlsclient.py**
import socket, ssl
import multiprocessing
class SubProc:
def __init__(self, sock):
self.sock = sock
def do(self):
self.sock.write("Test")
s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
ssl_sock = ssl.wrap_socket(s)
ssl_sock.connect(('127.0.0.1', 9998))
print "Connected to", repr(ssl_sock.getpeername())
for x in (1,2):
subproc = SubProc(ssl_sock)
proc = multiprocessing.Process(target=subproc.do)
And this is the backtrace:
Traceback (most recent call last):
File "tlsserver.py", line 21, in <module>
deal_with_client(connstream)
File "tlsserver.py", line 7, in deal_with_client
data = connstream.read()
File "/usr/lib64/python2.6/ssl.py", line 136, in read
return self._sslobj.read(len)
ssl.SSLError: [Errno 1] _ssl.c:1325: error:1408F119:SSL routines:SSL3_GET_RECORD:decryption failed or bad record mac
Answer: The problem is that you're re-using the same connection for both processes.
The way SSL encrypts data makes this fail -- the two processes would have to
communicate with each other about the state of the shared SSL connection. Even
if you do make it work, or if you didn't use SSL, the data would arrive at the
server all jumbled up; you would have no real way of distinguishing which
bytes came from which process.
What you need to do is give each process its own SSL connection, by making the
connection in `subproc.do`. Alternatively, don't have the subprocesses
communicate with the server at all, but rather communicate with the main
process, and have the main process relay it over the SSL connection.
|
Using Python quick insert many columns into Sqlite\Mysql
Question: If Newdata is list of x columns, How would get the number unique columns--
number of members of first tuple. (Len is not important.) Change the number of
"?" to match columns and insert using the statement below.
csr = con.cursor()
csr.execute('Truncate table test.data')
csr.executemany('INSERT INTO test.data VALUES (?,?,?,?)', Newdata)
con.commit()
Answer: By "Newdata is list of x columns", I imagine you mean `x` **tuples** , since
then you continue to speak of "the first tuple". If `Newdata` is a list of
tuples, `y = len(Newdata[0])` is the number of items in the first one of those
tuples.
Assuming that's the number you want (and all tuples had better have the same
number of items, otherwise `executemany` _will_ fail!), the general idea in
@Nathan's answer is right: build the string with the appropriate number of
comma-separated question marks:
holders = ','.join('?' * y)
then insert it in the rest of the SQL statement. @Nathan's way to insert is
right for most Python 2.any versions, but if you have 2.6 or better,
sql = 'INSERT INTO testdata VALUES({0})'.format(holders)
is currently preferred (it also works in Python 3.any).
Finally,
csr.executemany(sql, Newdata)
will do what you desire. Remember to commit the transaction once you're
done!-)
|
Prototype for python?
Question: I just learned Prototype for Javascript. It's super convenient: using the $
shortcut, accessing xml elements is not painful any more!
The question: is there a Prototype-like extension for Python?
Answer: Python has [lxml](http://codespeak.net/lxml/) which has the `xpath` method
wherein you could use xpath expressions to select elements. As I understand
it, $ in prototype searches and returns an element that has a particular id,
in which case could be translated in xpath to `*[@id=<someid>]` like so:
>>> import lxml.etree
>>> tree = lxml.etree.XML("<root><a id='1'/><b id='2'/></root>")
>>> tree.xpath("*[@id=1]")
[<Element a at c3bc30>]
>>> lxml.etree.tostring(tree.xpath("*[@id=1]")[0])
'<a id="1"/>'
I think the Python standard library includes support for a subset of xpath in
ElementTree too so you might be able to implement that there somehow if you do
not wish to install lxml (which isn't included in stdlib)...
|
Python subprocess timeout?
Question: Is there any argument or options to setup a timeout for Python's
subprocess.Popen method?
Something like this:
`subprocess.Popen(['..'], ..., timeout=20)` ?
Answer: I would advise taking a look at the [Timer
class](http://docs.python.org/2/library/threading.html#threading.Timer) in the
threading module. I used it to implement a timeout for a Popen.
First, create a callback:
def timeout( p ):
if p.poll() is None:
print 'Error: process taking too long to complete--terminating'
p.kill()
Then open the process:
proc = Popen( ... )
Then create a timer that will call the callback passing the process to it.
t = threading.Timer( 10.0, timeout, [proc] )
t.start()
t.join()
Somewhere later in the program, you may want to add the line:
t.cancel()
Otherwise, the python program will keep running until the timer has finished
running.
EDIT: I was advised that there is a race condition that the subprocess p may
terminate between the p.poll() and p.kill() calls. I believe the following
code can fix that:
import errno
def timeout( p ):
if p.poll() is None:
try:
p.kill()
print 'Error: process taking too long to complete--terminating'
except OSError as e:
if e.errno != errno.ESRCH:
raise
Though you may want to clean the exception handling to specifically handle
just the particular exception that occurs when the subprocess has already
terminated normally.
|
Is this a good reason to check types in Python?
Question: I know that checking types in Python is bad and you should probably never do
it. But I can't seem to find the disadvantage to this.
class O(object):
def __init__(self, name):
'''Can only be called in derived classes.'''
if type(self) is O:
message = "%(class)s cannot be instantiated, it must be derived."
raise TypeError, message % { "class" : O }
self.name = name
def fn(self):
'''Must be populated in derived classes.'''
raise NotImplementedError
Now if someone tries to instantiate O, a class I never meant to be
instantiated, they know immediately.
Is this still bad form?
Answer: Look at [Abstract Base Classes](http://docs.python.org/library/abc.html) as
they will provide more fine grained control over how the subclasses are
instantiated if this is something that you really want to do.
All in all, this might be a valid use because you are not preventing _me_ from
passing whatever _I_ want to your code but I still wouldn't consider it
pythonic. You are telling _me_ that _I_ can't instantiate your class. What If
I want to?
Using ABC's, it looks like:
import abc
class O(object):
__metaclass__ = abc.ABCMeta
def __init__(self, name):
self.name = name
@abc.abstractmethod
def fn(self):
pass
This has the advantage of not breaking super on the `fn` method. As you have
it with the `raise NotImplementedError`, you are breaking super for multiple
inheritance. If a class derives from two classes that subclass `O` and both
call super (as they should to allow for multiple inheritance) then it will
create the exception that you raise.
So now, you are not just telling me that I can't instantiate your class, you
are telling me that I can't use multiple inheritance when subclassing from
your class.
|
Getting pdb in Emacs to use Python process from current virtualenv
Question: I am debugging some python code in emacs using pdb and getting some import
issues. The dependencies are installed in one of my bespoked virtualenv
environments.
Pdb is stubbornly using /usr/bin/python and not the python process from my
virtualenv.
I use virtualenv.el to support switching of environments within emacs and via
the postactivate hooks described in
<http://jesselegg.com/archives/2010/03/14/emacs-python-
programmers-2-virtualenv-ipython-daemon-mode/>
This works well when running M-x python-shell
>>> import sys
>>> print sys.path
This points to all of my virtualenv libraries indicating that the python-shell
is that of my virtualenv.
This is contradicted however by M-! which python, which gives
_/usr/bin/python_
Does anyone know how I can tell M-x pdb to adopt the python process from the
currently active virtualenv?
Answer: `python-shell` uses variable `python-default-interpreter` to determine which
python interpreter to use. When the value of this variable is `cpython`, the
variables `python-python-command` and `python-python-command-args` are
consulted to determine the interpreter and arguments to use. Those two
variables are manipulated by `virtualenv.el` to set the current virtual
environment.
So when you use `python-shell` command, it uses your virtual environments
without any problem.
But, when you do `M-!` `python`, you're not using the variables `python-
python-command` and `python-python-command-args`. So it uses the python tools
it finds in your path.
When you call `M-x` `pdb` it uses gud-pdb-command-name as the default pdb
tool. To redefine this variable, each time you activate an environment, you
could do something like this :
(defadvice virtualenv-activate (after virtual-pdb)
(custom-set-variables
'(gud-pdb-command-name
(concat virtualenv-active "/bin/pdb" ))))
(ad-activate 'virtualenv-activate)
To have pdb in your virtual environment, do the following :
cp /usr/bin/pdb /path/to/virtual/env/bin
Then edit the first line of /path/to/virtual/env/bin/pdb to have :
#! /usr/bin/env python
Reactivate your env and Pdb should now use your virtualenv python instead of
the system-wide python.
|
How do you convert a stringed dictionary to a Python dictionary?
Question: I have the following string which is a Python dictionary stringified:
some_string = '{123: False, 456: True, 789: False}'
How do I get the Python dictionary out of the above string?
Answer: Use
[**`ast.literal_eval`**](http://docs.python.org/library/ast.html#ast.literal_eval):
> Safely evaluate an expression node or a string containing a Python
> expression. The string or node provided may only consist of the following
> Python literal structures: strings, numbers, tuples, lists, dicts, booleans,
> and None.
>
> This can be used for safely evaluating strings containing Python expressions
> from untrusted sources without the need to parse the values oneself.
Example:
>>> some_string = '{123: False, 456: True, 789: False}'
>>> import ast
>>> ast.literal_eval(some_string)
{456: True, 123: False, 789: False}
|
i got this error: "ImportError: cannot import name python" How do I fix it?
Question:
File "G:\Python25\Lib\site-packages\PyAMF-0.6b2-py2.5-win32.egg\pyamf\util\__init__.py", line 15, in <module>
ImportError: cannot import name python
How do I fix it? If you need any info to know how to fix this problem, I can
explain, just ask.
Thanks
Code:
from google.appengine.ext.webapp.util import run_wsgi_app
from google.appengine.ext import webapp
from TottysGateway import TottysGateway
import logging
def main():
services_root = 'services'
#services = ['users.login']
#gateway = TottysGateway(services, services_root, logger=logging, debug=True)
#app = webapp.WSGIApplication([('/', gateway)], debug=True)
#run_wsgi_app(app)
if __name__ == "__main__":
main()
Code:
from pyamf.remoting.gateway.google import WebAppGateway
import logging
class TottysGateway(WebAppGateway):
def __init__(self, services_available, root_path, not_found_service, logger, debug):
# override the contructor and then call the super
self.services_available = services_available
self.root_path = root_path
self.not_found_service = not_found_service
WebAppGateway.__init__(self, {}, logger=logging, debug=True)
def getServiceRequest(self, request, target):
# override the original getServiceRequest method
try:
# try looking for the service in the services list
return WebAppGateway.getServiceRequest(self, request, target)
except:
pass
try:
# don't know what it does but is an error for now
service_func = self.router(target)
except:
if(target in self.services_available):
# only if is an available service import it's module
# so it doesn't access services that should be hidden
try:
module_path = self.root_path + '.' + target
paths = target.rsplit('.')
func_name = paths[len(paths) - 1]
import_as = '_'.join(paths) + '_' + func_name
import_string = "from "+module_path+" import "+func_name+' as service_func'
exec import_string
except:
service_func = False
if(not service_func):
# if is not found load the default not found service
module_path = self.rootPath + '.' + self.not_found_service
import_string = "from "+module_path+" import "+func_name+' as service_func'
# add the service loaded above
assign_string = "self.addService(service_func, target)"
exec assign_string
return WebAppGateway.getServiceRequest(self, request, target)
Answer: You need to post your full traceback. What you show here isn't all that
useful. I ended up digging up line 15 of pyamf/util/**init**.py. The code you
should have posted is
from pyamf import python
This should not fail unless your local environment is messed up.
Can you 'import pyamf.util' and 'import pyamf.python' in a interactive Python
shell? What about if you start Python while in /tmp (on the assumption that
you might have a file named 'pyamf.py' in the current directory. Which is a
bad thing.)
= (older comment below) =
Fix your question. I can't even tell where line 15 of util/__init__.py is
supposed to be. Since I can't figure that out, I can't answer your question.
Instead, I'll point out ways to improve your question and code.
First, use the markup language correctly, so that all the code is in a code
block. Make sure you've titled the code, so we know it's from util/__init__.py
and not some random file.
In your error message, include the _full_ traceback, and not the last two
lines.
Stop using parens in things like "if(not service_func):" and use a space
instead, so its " if not service_func:". This is discussed in [PEP
8](http://www.python.org/dev/peps/pep-0008/).
Read the Python documentation and learn how to use the language. Something
like "func_name = paths[len(paths) - 1]" should be "func_name = paths[-1]"
Learn about the
[**import**](http://docs.python.org/library/functions.html#__import__)
function and don't use "exec" for this case. Nor do you need the "exec
assign_string" -- just do the "self.addService(service_func, target)"
|
WxPython - Resize WxFrame when adding new content?
Question: Pretty much exactly as it sounds. I have buttons in a `Wx.Frame` that are
created on the fly and I'd like the parent frame to increase in height as I
add new buttons. The height is already being acquire from the total number of
buttons multiplied by an integer equal the each button's height, but I don't
know how to get the frame to change size based on that when new buttons are
added.
As a side question the current method I have for updating the buttons creates
a nasty flicker and I was wondering if anyone had any ideas for fixing that.
import wx
import mmap
import re
class pt:
with open('note.txt', "r+") as note:
buf = mmap.mmap(note.fileno(), 0)
TL = 0
readline = buf.readline
while readline():
TL += 1
readlist = note.readlines()
note.closed
class MainWindow(wx.Frame):
def __init__(self, parent, title):
w, h = wx.GetDisplaySize()
self.x = w * 0
self.y = h - bdepth
self.container = wx.Frame.__init__(self, parent, title = title, pos = (self.x, self.y), size = (224, bdepth), style = wx.STAY_ON_TOP)
self.__DoButtons()
self.Show(True)
def __DoButtons(self):
for i, line in enumerate(pt.readlist):
strip = line.rstrip('\n')
todo = strip.lstrip('!')
self.check = re.match('!', strip)
self.priority = re.search('(\!$)', strip)
if self.check is None and self.priority is None:
bullet = wx.Image('bullet.bmp', wx.BITMAP_TYPE_BMP)
solid = wx.EmptyBitmap(200,64,-1)
dc = wx.MemoryDC()
dc.SelectObject(solid)
solidpen = wx.Pen(wx.Colour(75,75,75),wx.SOLID)
dc.SetPen(solidpen)
dc.DrawRectangle(0, 0, 200, 64)
dc.SetTextForeground(wx.Colour(255, 255, 255))
dc.DrawBitmap(wx.BitmapFromImage(bullet, 32), 10, 28)
dc.DrawText(todo, 30, 24)
dc.SelectObject(wx.NullBitmap)
hover = wx.EmptyBitmap(200,64,-1)
dc = wx.MemoryDC()
dc.SelectObject(hover)
hoverpen = wx.Pen(wx.Colour(100,100,100),wx.SOLID)
dc.SetPen(hoverpen)
dc.DrawRectangle(0, 0, 200, 64)
dc.SetTextForeground(wx.Colour(255, 255, 255))
dc.DrawBitmap(wx.BitmapFromImage(bullet, 32), 10, 28)
dc.DrawText(todo, 30, 24)
dc.SelectObject(wx.NullBitmap)
bmp = solid
elif self.priority is None:
checkmark = wx.Image('check.bmp', wx.BITMAP_TYPE_BMP)
checked = wx.EmptyBitmap(200,64,-1)
dc = wx.MemoryDC()
dc.SelectObject(checked)
checkedpen = wx.Pen(wx.Colour(50,50,50),wx.SOLID)
dc.SetPen(checkedpen)
dc.DrawRectangle(0, 0, 200, 50)
dc.SetTextForeground(wx.Colour(200, 255, 0))
dc.DrawBitmap(wx.BitmapFromImage(checkmark, 32), 6, 24)
dc.DrawText(todo, 30, 24)
dc.SelectObject(wx.NullBitmap)
bmp = checked
else:
exclaim = wx.Image('exclaim.bmp', wx.BITMAP_TYPE_BMP)
important = wx.EmptyBitmap(200,64,-1)
dc = wx.MemoryDC()
dc.SelectObject(important)
importantpen = wx.Pen(wx.Colour(75,75,75),wx.SOLID)
dc.SetPen(importantpen)
dc.DrawRectangle(0, 0, 200, 50)
dc.SetTextForeground(wx.Colour(255, 180, 0))
dc.DrawBitmap(wx.BitmapFromImage(exclaim, 32), 6, 24)
dc.DrawText(todo, 30, 24)
dc.SelectObject(wx.NullBitmap)
importanthover = wx.EmptyBitmap(200,64,-1)
dc = wx.MemoryDC()
dc.SelectObject(importanthover)
importanthoverpen = wx.Pen(wx.Colour(100,100,100),wx.SOLID)
dc.SetPen(importanthoverpen)
dc.DrawRectangle(0, 0, 200, 50)
dc.SetTextForeground(wx.Colour(255, 180, 0))
dc.DrawBitmap(wx.BitmapFromImage(exclaim, 32), 6, 24)
dc.DrawText(todo, 30, 24)
dc.SelectObject(wx.NullBitmap)
bmp = important
b = wx.BitmapButton(self, i + 800, bmp, (10, i * 64), (bmp.GetWidth(), bmp.GetHeight()), style = wx.NO_BORDER)
if self.check is None and self.priority is None:
b.SetBitmapHover(hover)
elif self.priority is None:
b.SetBitmapHover(checked)
else:
b.SetBitmapHover(importanthover)
self.input = wx.TextCtrl(self, -1, "", (16, pt.TL * 64 + 4), (184, 24))
self.Bind(wx.EVT_TEXT_ENTER, self.OnEnter, self.input)
def OnClick(self, event):
button = event.GetEventObject()
button.None
print('cheese')
def OnEnter(self, event):
value = self.input.GetValue()
pt.readlist.append('\n' + value)
self.__DoButtons()
with open('note.txt', "r+") as note:
for item in pt.readlist:
note.write("%s" % item)
note.closed
bdepth = pt.TL * 64 + 32
app = wx.App(False)
frame = MainWindow(None, "Sample editor")
app.SetTopWindow(frame)
app.MainLoop()
Answer: **Don't** double-prefix your methods unless you know what you're doing. This
is not directly related to your question, but it'll result in bugs you won't
understand later.
See this [stackoverflow](http://stackoverflow.com/questions/1301346/the-
meaning-of-a-single-and-a-double-underscore-before-an-object-name-in-python)
question and [the python
documentation](http://docs.python.org/tutorial/classes.html#private-variables)
what/why.
|
Is there some website that has examples of every method in the python standard library?
Question: For example, c++ have
[cplusplus.com/reference](http://cplusplus.com/reference) which contain all of
c++ standard library complete with definitions and more importantly examples,
so I was wondering if there is such a website for python. I know that python
is self documented, like i could use
help(object)
object.__doc__
dir(object)
I know of
[doc.python.org/library](http://doc.python.org/library)
[wiki.python.org](http://wiki.python.org)
But it doesn't have examples of every method. It would be nice if there was
such a website, because when I am learning a new python library I find myself
just testing the methods to see if it does what I want, and it makes my
programming really slow. But this maybe because I have only have 2 years of
programming under my belt. So my question is, is there such a website and is
there a better way to learning a new library in python? Because when learning
a new c++ library, all I need to do is follow by example which makes learning
a new c++ library really easy.
Answer: Try [Python Module of The
Week](http://www.doughellmann.com/PyMOTW/contents.html). It may not be exactly
what your looking for, but you should find it helpfull.
> PyMOTW is a series of blog posts written by Doug Hellmann. It was started as
> a way to build the habit of writing something on a regular basis. The focus
> of the series is building a set of example code for the modules in the
> Python standard library.
|
Python meta-debugging
Question: Heyo,
Just started writing an assembler for the imaginary computer my class is
creating wire-by-wire since the one the TA's provided sucks hard. I chose
python even though I've never really used it that much (but know the basic
syntax) and am loving it.
My favorite ability is how I can take a method I just wrote, paste it into the
shell and then unit test it by hand (I'm using IDLE).
I'm just wondering if there is a way to expose all the symbols in my python
code to the shell automatically, so I can debug without copying and pasting my
code into the shell every time (especially when I make a modification in the
code).
Cheers
Answer: you can import the module that your code is in. This will expose all of the
symbols prefixed with the module name.
The details for the easiest way to do it depend on your operating system but
you can always do:
>>> sys.path.append('/path/to/directory/that/my/module/is/in/')
>>> import mymod #.py
later after you make a change, you can just do
>>>> reload(mymod)
and the symbols will now reference the new values. Note that `from mymod
import foo` will break `reload` in the sense that `foo` will _not_ be updated
after a call to `reload`. So just use `mymod.foo`.
Essentially the trick is to get the directory containing the file on your
`PYTHONPATH` environment variable. You can do this from .bashrc on linux for
example. I don't know how to go about doing it on another operating system. I
use [virualenv](http://pypi.python.org/pypi/virtualenv) with has a [nice
wrapper](http://www.doughellmann.com/projects/virtualenvwrapper/) and `workon`
command so I just have to type `workon foo` and it runs shell scripts (that I
had to write) that add the necessary directories to my python path.
When I was just starting off though, I made one permanent addition to my
`PYTHONPATH` env variable and kept module I wrote in there.
Another alternative is to execute your module with the `-i` option.
$ python -i mymod.py
This will execute the module through to completion and then leave you at the
interpreter. this isn't IDLE though, it's a little rougher but you are now in
your module's namespace (or rather the module's namespace is the global
namespace)
|
Do you think/write differently in vim and emacs?
Question: In many scripts that I write, I often construct programs in a "functional
style". That is to say, I basically define a lot of functions at the
beginning, and then later apply these functions. This results in a sequence of
nested function calls, wherein I type out:
1. function name
2. its arguments
3. next function name
4. its arguments
...and so on.
For cases in which functions are "piped" together, the output of one function
is an argument (usually the first, but not always) to the next function, the
output of which is an argument to the next function, and ad infinitum. In
prefix-notation, the key movements can be very jumpy if you type out this
sequence from left to right. For example, how would you type out the second
line of the following [Python] example (~mul~ is multiply, ~truediv~ is
divide)?
from operator import add, mul, truediv
print(truediv(mul(add(1,1),2),4))
If I had to write the same set of operations linearly (from left to write,
without jumping around), I am more likely to use the notation of function
composition. Building on my previous example in Python, I might write
from functional import foldr, compose, partial, flip
print(foldr(compose,add,(partial(mul,2),partial(flip(truediv),4)))(1,1))
I think this is because I associate each function with its own arguments and
prefer to type them out in succession, rather than filling arguments to
another function before the argument list for the first function is complete
(as would be required to type out the first example from left to right).
I noticed this because I've been an emacs user for a long time and only
recently tried out viper/vimpuse and vim. In emacs, I might do something like
1. [type function name and arguments]
2. C-a
3. [type next function name]
4. C-e
5. [fill in rest of arguments]
6. C-a
7. [type next function name]
8. C-e
9. [fill in rest of arguments]
...and so on, with occasional use of M-b, M-f, M-DEL (backward-word, forward-
word, backward-kill-word) if I mess up or forget something.
I recently found out about C-o in vim, which is a lifesaver - but I find that
the equivalent keys would be
1. [type function name and arguments]
2. C-o 0
3. [type next function name]
4. C-o $
5. [fill in rest of arguments]
6. C-o 0
7. [type next function name]
8. C-o $
9. [fill in rest of arguments]
...and the rest; backward-word, forward-word, and backward-kill-word
equivalents would be C-o b and C-o w, and C-w.
So this got me thinking that to program in vim, I may have to grow a larger
working memory, so that I can pause the construction of one function as I fill
out another, and so on down the stack. Also, in construcing text documents, I
find that I edit (kill, copy, yank) quite frequently even before I finish a
complete thought, which is not so amenable for vim's operational style of
"stay in normal mode, burst of text in insert-mode, and back to normal mode",
which seems to presume that I am capable of producing something worth editing
during my forays into insert-mode. To use vim, I find that I deliberate more
as I type to reduce the frequency of switching between modes. Is this because
I'm naturally spastic, or once I master or commit a suitable range of vim key
commands to muscle memory, I'll stop thinking they're so different?
If you program in both emacs and vim, do you find yourself thinking about and
construcing your programs and blocks of text differently in each editor?
Answer: I used vi from the good old days of 1992 and now I use Emacs since 2001. I
haven't noticed any difference in my thinking when programming functions and
blocks of code. Both editors has their own peculiarities and ways of doing
things, but they are not so strong that they could change your way of thinking
and how you program.
I've always tried to find ways to do what I intend to do. I don't let my
editor force me to do something I don't want. When I do procedural programming
of a new piece of code, I use the technique called "wishful thinking" that is
[mentioned in Structure and Interpretation of Computer
Programs](http://mitpress.mit.edu/sicp/full-text/sicp/book/node28.html) :
You imagine yourself in the perfect world having all the procedures you need
at your disposal. You code your algorithm with all those helpful functions
that you'll need to implement but that you only have prototypes for the
moment. It's similar to a top-down approach.
|
Python programming
Question: My assignment ask to make a function call readFasta that accepts one argument:
the name of a fasta format file (fn) containing one or more sequences. The
function should read the file and return a dictionary where the keys are the
fasta headers and the values are the corresponding sequences from file fn
converted to strings. Make sure that you don’t include any new lines or other
white space characters in the sequences in the dictionary.
For ex, if afile.fa looks like:
>one
atctac
>two
gggaccttgg
>three
gacattac
then the a.readFasta(f) returns:
[‘one’ : ‘atctac’,
‘two’ : ‘gggaccttgg’,
‘three’: ‘gacattac’]
If have tried to write some codes but as I am totally newbie in programming,
it didnt work out very much for me. Can everyone please help me. Thank you so
much. Here are my codes:
import gzip
def readFasta(fn):
if fn.endswith('.gz'):
fh = gzip.gzipfile(fn)
else:
fh = open(fn,'r')
d = {}
while 1:
line = fh.readline()
if not line:
fh.close()
break
vals = line.rstrip().split('\t')
number = vals[0]
sequence = vals[1]
if d.has_key(number):
lst = d[number]
if gene not in lst:
# this test may not be necessary
lst.append(sequence)
else:
d[number] = [sequence]
return d
Here is what I got in my afile.txt
> one atctac
>
> two gggaccttgg
>
> three gacattac
Answer: your post is slightly confusing. I assume that you want it to return a dict.
in that case, you would write it as `{'one': 'actg', 'two': 'aaccttgg' }`. if
you correctly presented the file format, then this function should do the
trick.
import gzip
def read_fasta(filename):
with gzip.open(filename) as f:
return dict(line.split() for line in f)
|
Connect Sphinx autodoc-skip-member to my function
Question: I want to use [sphinx's autodoc-skip-
member](http://sphinx.pocoo.org/ext/autodoc.html#event-autodoc-skip-member)
event to select a portion of the members on a certain python class for
documentation.
But it isn't clear from the sphinx docs, and I can't find any examples that
illustrate: where do I put the code to connect this? I see
[Sphinx.connect](http://sphinx.pocoo.org/ext/appapi.html#sphinx.application.Sphinx.connect)
and I suspect it goes in my conf.py, but when I try variations on this code in
conf.py I can't find the app object that I should connect():
def maybe_skip_member(app, what, name, obj, skip,
options):
print app, what, name, obj, skip, options
return False
# This is not even close to correct:
#from sphinx.application import Sphinx
#Sphinx().connect('autodoc-skip-member', maybe_skip_member)
A pointer to a simple example would be ideal.
Answer: Aha, last ditch effort on a little googling turned up [this
example](http://trac.sagemath.org/sage_trac/attachment/ticket/7813/conf.py),
scroll down to the bottom. Apparently a setup() function in conf.py will get
called with the app. I was able to define the following at the bottom of my
conf.py:
def maybe_skip_member(app, what, name, obj, skip, options):
print app, what, name, obj, skip, options
return True
def setup(app):
app.connect('autodoc-skip-member', maybe_skip_member)
Which is obviously useless (it skips everything), but that's the minimal
example I was looking for and couldn't find...
|
creating xml tree from a textfile with Python
Question: I need to avoid creating double branches in an xml tree when parsing a text
file. Let's say the textfile is as follows (the order of lines is random):
branch1:branch11:message11
branch1:branch12:message12
branch2:branch21:message21
branch2:branch22:message22
So the resulting xml tree should have a root with two branches. Both of those
branches have two subbranches. The Python code I use to parse this textfile is
as follows:
import string
fh = open ('xmlbasic.txt', 'r')
allLines = fh.readlines()
fh.close()
import xml.etree.ElementTree as ET
root = ET.Element('root')
for line in allLines:
tempv = line.split(':')
branch1 = ET.SubElement(root, tempv[0])
branch2 = ET.SubElement(branch1, tempv[1])
branch2.text = tempv[2]
tree = ET.ElementTree(root)
tree.write('xmlbasictree.xml')
The problem with this code is, that a branch in xml tree is created with each
line from the textfile.
Any suggestions how to avoid creating another branch in xml tree if a branch
with this name exists already?
Answer:
with open("xmlbasic.txt") as lines_file:
lines = lines_file.read()
import xml.etree.ElementTree as ET
root = ET.Element('root')
for line in lines:
head, subhead, tail = line.split(":")
head_branch = root.find(head)
if not head_branch:
head_branch = ET.SubElement(root, head)
subhead_branch = head_branch.find(subhead)
if not subhead_branch:
subhead_branch = ET.SubElement(branch1, subhead)
subhead_branch.text = tail
tree = ET.ElementTree(root)
ET.dump(tree)
The logic is simple -- you already stated it in your question! You merely need
to check whether a branch already exists in the tree before creating it.
Note that this is likely inefficient, since you are searching up to the entire
tree for each line. This is because `ElementTree` is not designed for
uniqueness.
* * *
If you require speed (which you may not, especially for smallish trees!), a
more efficient way would be to use a `defaultdict` to store the tree structure
before converting it to an `ElementTree`.
import collections
import xml.etree.ElementTree as ET
with open("xmlbasic.txt") as lines_file:
lines = lines_file.read()
root_dict = collections.defaultdict( dict )
for line in lines:
head, subhead, tail = line.split(":")
root_dict[head][subhead] = tail
root = ET.Element('root')
for head, branch in root_dict.items():
head_element = ET.SubElement(root, head)
for subhead, tail in branch.items():
ET.SubElement(head_element,subhead).text = tail
tree = ET.ElementTree(root)
ET.dump(tree)
|
Is there a way to run a python script that is inside a zip file from bash?
Question: I know there is a way to import modules which are in a zip file with python. I
created kind of custom python package library in a zip file.
I would like to put as well my "task" script in this package, those are using
the library. Then, with bash, I would like to call the desired script in the
zip file without extracting the zip.
The goal is to have only one zip to move in a specified folder when I want to
run my scripts.
Answer: I finally found a way to do this. If I create a zip file, I must create
`__main__.py` at the root of the zip. Thus, it is possible to launch the
script inside the main and call if from bash with the following command :
`python myArchive.zip`
This command will run the `__main__.py` file! :)
Then I can create `.command` file to launch the script with proper parameters.
You can also put some code in the `__main__.py` file to give you more
flexibility if you need to pass arguments for example.
ex: `python __main__.py buildProject`
The reference documentation is here:
<https://docs.python.org/2/library/runpy.html>
|
On Google App Engine (GAE), how do I search on the Key/ID field?
Question: I've got this code (Java, GAE):
// Much earlier:
playerKey = KeyFactory.keyToString(somePlayer.key);
// Then, later...
PersistenceManager pm = assassin.PMF.get().getPersistenceManager();
Key targetKey = KeyFactory.stringToKey(playerKey);
Query query = pm.newQuery(Player.class);
query.setFilter("__key__ == keyParam");
query.declareParameters("com.google.appengine.api.datastore.Key keyParam");
List<Player> players = (List<Player>) query.execute(targetKey); // <-- line 200
which generates this error:
javax.jdo.JDOFatalUserException: Unexpected expression type while parsing query. Are you certain that a field named __key__ exists on your object?
at org.datanucleus.jdo.NucleusJDOHelper.getJDOExceptionForNucleusException(NucleusJDOHelper.java:354)
at org.datanucleus.jdo.JDOQuery.execute(JDOQuery.java:252)
at myapp.Player.validPlayerWithKey(Player.java:200)
// [etc., snip]
But I'm not sure what it wants. I'm trying to search on the JDO id field,
which I I thought I read had the special name `__key__`, [in the
documentation](http://code.google.com/appengine/docs/python/datastore/gqlreference.html).
I've tried it with both
query.setFilter("__key__ == keyParam");
and
query.setFilter("ID == keyParam");
with the same results. So, what am I doing wrong? Or, more importantly, how do
I do it correctly?
Thanks!
**Edit:** For completeness's sake, here is the final, working code (based on
Gordon's answer, which I have accepted as correct):
Player result = null;
if (playerKey == null)
{
log.log(Level.WARNING, "Tried to find player with null key.");
}
else
{
PersistenceManager pm = assassin.PMF.get().getPersistenceManager();
try {
result = (Player) pm.getObjectById(Player.class, playerKey);
} catch (javax.jdo.JDOObjectNotFoundException notFound) {
// Player not found; we will return null.
result = null;
}
pm.close();
}
return result;
Answer: If your objective is to get an object by key, then you should use the
PersistenceManager's getObjectByID() method. More details
[here](http://code.google.com/appengine/docs/java/datastore/creatinggettinganddeletingdata.html#Getting_an_Object_By_Key).
As an aside, trying to construct a query to get something by it's key is
something you shouldn't need to do. Although this is how you would work with
an SQL database, the Google Data Store does things differently, and this is
one of those cases where rather than go through the trouble of constructing a
query, Google App Engine lets you get what you want directly. After all, you
should only have one entity in the database with a particular key, so there's
nothing in the rest of the machinery of a GQL query that you need in this
case, hence it can all be skipped for efficiency.
|
How to make a .exe for Python with good graphics?
Question: I have a Python application and I decided to do a .exe to execute it.
This is the code that I use to do the .exe:
# -*- coding: cp1252 -*-
from distutils.core import setup
import py2exe, sys, os
sys.argv.append('py2exe')
setup(
options = {'py2exe': {'bundle_files': 1}},
windows = [{'script': "SoundLog.py"}],
zipfile = None,
packages=[r"C:\Users\Public\SoundLog\Code\Código Python\SoundLog\Auxiliar", r"C:\Users\Public\SoundLog\Code\Código Python\SoundLog\Plugins"],
)
But when I run my application with the .exe, the graphics are quite different.
In the image bellow you can see the application running thought python at the
left and running thought the .exe at the right. 
How can I make the .exe one be as good as the one that runs thought python?
Answer: I assume you mean the visual style of the toolbar and buttons. You need to add
a manifest file to the EXE file or as a separate file so that Windows applies
the modern style of recent comctl32.dll versions.
Check out [Using Windows XP Visual Styles With Controls on Windows
Forms](http://msdn.microsoft.com/en-us/library/aa289524%28VS.71%29.aspx) on
MSDN. Read the relevant part about creating the ".exe.manifest" file.
A more py2exe-specific tutorial can be found over at the [wxPython
site](http://wiki.wxpython.org/DistributingYourApplication). They explain how
to use setup.py to include the necessary manifest file.
|
Run Python CGI Script on Windows XP
Question: This exact question has been asked before but I am at my wits end! I've spend
4 hours trying to get a SIMPLE Python CGI script to work on Windows XP but I
get errors. Please save my sanity!
Python Script register.py
#!c:/Python30/python.exe -u
print "Content-type: text/html"
print "<P>Hello, World!</p>"
Script is located in:
C:\Program Files\Apache Software Foundation\Apache2.2\cgi-bin\alerter
Apache Error Log:
[Tue Sep 21 19:06:36 2010] [error] [client 127.0.0.1] Premature end of script headers: register.py
[Tue Sep 21 19:06:36 2010] [error] [client 127.0.0.1] File "C:/Program Files/Apache Software Foundation/Apache2.2/cgi-bin/alerter/register.py", line 3\r
[Tue Sep 21 19:06:36 2010] [error] [client 127.0.0.1] print "Content-type: text/html"\r
[Tue Sep 21 19:06:36 2010] [error] [client 127.0.0.1] ^\r
[Tue Sep 21 19:06:36 2010] [error] [client 127.0.0.1] SyntaxError: invalid syntax\r
httpd.conf:
LoadModule cgi_module modules/mod_cgi.so
<Directory "C:/Program Files/Apache Software Foundation/Apache2.2/cgi-bin">
AllowOverride None
Options None
Order allow,deny
Allow from all
Options +ExecCGI
AddHandler cgi-script .py
</Directory>
This should be VERY simple. Yes? I mus be missing that ONE thing that will
make it finally work. I got PHP working a while back with no problems.
Any ideas? Thanks!!!
Answer: Your error is:
> Premature end of script headers
Note that the HTTP protocol specifies that the body of a HTTP response is
separated from it's headers by a blank line (i.e. two times a carriage return
and line feed). I'd go for something like:
import sys
sys.stdout.write("Content-type: text/html\r\n\r\n<p>Body</p>")
|
Python function to solve Ax = b by back substitution
Question: Okay, for my numerical methods class I have the following question:
Write a Python function to solve Ax = b by back substitution, where A is an
upper triangular nonsingular matrix. MATLAB code for this is on page 190 which
you can use as a pseudocode guide if you wish. The function should take as
input A and b and return x. Your function need not check that A is
nonsingular. That is, assume that only nonsingular A will be passed to your
function.
The MATLAB code that it refers to is:
x(n) = c(u)/U(n,n)
for i = n-1 : -1 : 1
x(i) = c(i);
for j = i+1 : n
x(i) = x(i) - U(i,j)*x(j);
end
x(i) = x(i)/U(i,i);
end
My Python code, which I wrote using the MATLAB code snippet, is with an upper
triangular test matrix(not sure if its nonsingular! How do I test for
singularity?):
from scipy import mat
c=[3,2,1]
U=([[6,5,1],[0,1,7],[0,0,2]])
a=0
x=[]
while a<3:
x.append(1)
a=a+1
n=3
i=n-1
x[n-1]=c[n-1]/U[n-1][n-1]
while i>1:
x[i]=c[i]
j=i+1
while j<n-1:
x[i]=x[i]-U[i][j]*x[j];
x[i]=x[i]/U[i][i]
i=i-1
print mat(x)
The answer I am getting is [[1 1 0]] for x. I not sure if I am doing this
correctly. I assume it is wrong and can't figure out what to do next. Any
clues?
Answer:
j=i+1
while j<n-1:
x[i]=x[i]-U[i][j]*x[j];
is infinite ... and never gets executed
your indexing is fubared:
for i in range(n-2,-1,-1):
....
for j in range(i+1,n):
notice, range is half open unlike matlab
|
Python text validation: a-z and comma (",")
Question: I need to check that some text only contains lower-case letters a-z and a
comma (",").
What is the best way to do this in Python?
Answer:
import re
def matches(s):
return re.match("^[a-z,]*$", s) is not None
Which gives you:
>>> matches("tea and cakes")
False
>>> matches("twiddledee,twiddledum")
True
You can optimise a bit with re.compile:
import re
matcher = re.compile("^[a-z,]*$")
def matches(s):
return matcher.match(s) is not None
|
Namespaces in C# vs imports in Java and Python
Question: In the Java and Python world, you look at a source file and know where all the
imports come from (i.e. you know in which file the imported classes are
defined). For example:
In Java:
import javafoo.Bar;
public class MyClass {
private Bar myBar = new Bar();
}
You immediately see that the Bar-class is imported from javafoo. So, Bar is
declared in `/javafoo/Bar.java`
In Python
import pythonbaz
from pythonfoo import Bar
my_bar = Bar()
my_other = pythonbaz.Other()
Here, it is clear that Bar comes from the pythonfoo package and Other is
obviously from pythonbaz.
In C# (correct me if I'm wrong):
using foo
using baz
using anothernamespace
...
public class MyClass
{
private Bar myBar = new Bar();
}
Two questions:
1) How do I know where the Bar-class is declared? Does it come from the
namespace `foo`, or `bar`, or `anothernamespace`? (edit: **without** using
Visual Studio)
2) In Java, the package names correspond to directory names (or, it is a very
strong convention). Thus, when you see which package a class comes from, you
know its directory in the file system.
In C#, there does not seem to be such a convention for namespaces, or am I
missing something? So, how do I know which directory and file to look in
(without Visual Studio)? (after figuring out which namespace the class came
from).
**Edit clarification** : I am aware that Python and/or Java allow wildcard
imports, but the 'culture' in those languages frowns upon them (at least in
Python, in Java I'm not sure). Also, in Java IDEs usually help you create
minimal imports (as Mchl. commented below)
Answer: 1) Well, you can do the same thing in Java too:
import java.util.*;
import java.io.*;
...
InputStream x = ...;
Does `InputStream` come from `java.util` or `java.io`? Of course, you can
choose not to use that feature.
Now, in _theory_ I realise this means when you're looking with a text editor,
you can't tell where the types come from in C#... but in practice, I don't
find that to be a problem. How often are you _actually_ looking at code and
can't use Visual Studio?
2) You can use the same convention in .NET too, of course - and I do, although
I don't have empty directories going up the chain... so if I'm creating a
project with a default namespace of X.Y, then `X.Y.Foo` would be in `Foo.cs`,
and X.Y.Z.Bar would be in `Z\Bar.cs`
That's also what Visual Studio will do by default - if you create a subfolder,
it will create new classes using a namespace based on the project default and
the folder structure.
Of course, you can also declare types in any old file - but _mostly_ people
will follow the normal convention of declaring a type with a corresponding
filename. Before generics made delegate declarations rarer, I used to have a
`Delegates.cs` file containing all the delegate declarations for a particular
namespace (rather than having a bunch of single-declaration files) but these
days that's less of an issue.
|
How to reload modules in django shell?
Question: I am working with Django and use Django shell all the time. The annoying part
is that while the Django server reloads on code changes, the shell does not,
so every time I make a change to a method I am testing, I need to quit the
shell and restart it, re-import all the modules I need, reinitialize all the
variables I need etc. While iPython history saves a lot of typing on this,
this is still a pain. Is there a way to make django shell auto-reload, the
same way django development server does?
I know about reload(), but I import a lot of models and generally use `from
app.models import *` syntax, so reload() is not much help.
Answer: look at the manage.py shell_plus command provided by the [django-
extensions](https://github.com/django-extensions/django-extensions) project.
It will load all your model files on shell startup. and autoreload your any
modify but do not need exit, you can direct call there
|
How can I selectively mask arbitrary data being sent over an insecure link?
Question: I'm using an offsite error logging package for my python web application. When
I send an error I include the contents of (among other things) the POST
variable and some template data. Some of this data must not be sent to the
error logging service (passwords, some other template data).
How can I take a payload that consists of a mix of data -- objects, dicts, et
al -- and mask out (say) every field or entry named `my_private_data`?
What I'd expect is that if an object has a string or integer property (the
private data will always be a number or a string) `my_private_data=SOME
SECRET`, it would be transmitted as `my_private_data=**********`
How do I accomplish this?
Answer: If you have the POST data as a string, you can use the standard modules
"urlparse" and "urllib" to remove certain parameters:
import urlparse
import urllib
postDataAsDict = urlparse.parse_qs("a=5&b=3&c=%26escaped", strict_parsing = True)
print postDataAsDict # prints {'a': ['5'], 'b': ['3'], 'c': ['&escaped']}
del postDataAsDict["a"] # in your case "my_private_data"
print urllib.urlencode(postDataAsDict, True) # prints c=%26escaped&b=3
Note that `parse_qs` correctly supports multiple parameters that have the same
name, so don't worry about that.
|
free implementation of counting user sessions from a web server log?
Question: Web server log analyzers (e.g. Urchin) often display a number of "sessions". A
session is defined as a series of page visits / clicks made by an individual
within a limited, continuous time segment. The attempt is made to identify
these segments using IP addresses, and often supplementary info like user
agent and OS, along with a session timeout threshold such as 15 or 30 minutes.
For certain web sites and applications, a user can be logged in and/or tracked
with a cookie, which means the server can precisely know when a session
begins. I'm not talking about that, but about inferring sessions heuristically
("[session
reconstruction](http://www.dblab.ntua.gr/persdl2007/papers/72.pdf)") when the
web server does not track them.
I could write some code e.g. in Python to try to reconstruct sessions based on
the criteria mentioned above, but I'd rather not reinvent the wheel. I'm
looking at log files of a size around 400K lines, so I'd have to be careful to
use a scalable algorithm.
My goal here is to extract a list of unique IP addresses from a log file, and
for each IP address, to have the number of sessions inferred from that log.
Absolute precision and accuracy are not necessary... pretty-good estimates are
ok.
Based on [this
description](http://www.dblab.ntua.gr/persdl2007/papers/72.pdf):
> a new request is put in an existing session if two conditions are valid:
>
> * the IP address and the user-agent are the same of the requests already
> inserted in the session,
> * the request is done less than fifteen minutes after the last request
> inserted.
>
it would be simple in theory to write a Python program to build up a
dictionary (keyed by IP) of dictionaries (keyed by user-agent) whose value is
a pair: (number of sessions, latest request of latest session).
But I would rather try to use an existing implementation if one's available,
since I might otherwise risk spending a lot of time tuning performance.
FYI lest someone ask for sample input, here is a line of our log file
(sanitized):
#Fields: date time s-ip cs-method cs-uri-stem cs-uri-query s-port cs-username c-ip cs(User-Agent) cs(Referer) sc-status sc-substatus sc-win32-status
2010-09-21 23:59:59 215.51.1.119 GET /graphics/foo.gif - 80 - 128.123.114.141 Mozilla/5.0+(Windows;+U;+Windows+NT+5.1;+en-US;+rv:1.9.2)+Gecko/20100115+Firefox/3.6+(.NET+CLR+3.5.30729) http://www.mysite.org/blarg.htm 200 0 0
Answer: OK, in the absence of any other answer, here's my Python implementation. I'm
not a Python expert. Suggestions for improvement are welcome.
#!/usr/bin/env python
"""Reconstruct sessions: Take a space-delimited web server access log
including IP addresses, timestamps, and User Agent,
and output a list of the IPs, and the number of inferred sessions for each."""
## Input looks like:
# Fields: date time s-ip cs-method cs-uri-stem cs-uri-query s-port cs-username c-ip cs(User-Agent) cs(Referer) sc-status sc-substatus sc-win32-status
# 2010-09-21 23:59:59 172.21.1.119 GET /graphics/foo.gif - 80 - 128.123.114.141 Mozilla/5.0+(Windows;+U;+Windows+NT+5.1;+en-US;+rv:1.9.2)+Gecko/20100115+Firefox/3.6+(.NET+CLR+3.5.30729) http://www.site.org//baz.htm 200 0 0
import datetime
import operator
infileName = "ex100922.log"
outfileName = "visitor-ips.csv"
ipDict = {}
def inputRecords():
infile = open(infileName, "r")
recordsRead = 0
progressThreshold = 100
sessionTimeout = datetime.timedelta(minutes=30)
for line in infile:
if (line[0] == '#'):
continue
else:
recordsRead += 1
fields = line.split()
# print "line of %d records: %s\n" % (len(fields), line)
if (recordsRead >= progressThreshold):
print "Read %d records" % recordsRead
progressThreshold *= 2
# http://www.dblab.ntua.gr/persdl2007/papers/72.pdf
# "a new request is put in an existing session if two conditions are valid:
# * the IP address and the user-agent are the same of the requests already
# inserted in the session,
# * the request is done less than fifteen minutes after the last request inserted."
theDate, theTime = fields[0], fields[1]
newRequestTime = datetime.datetime.strptime(theDate + " " + theTime, "%Y-%m-%d %H:%M:%S")
ipAddr, userAgent = fields[8], fields[9]
if ipAddr not in ipDict:
ipDict[ipAddr] = {userAgent: [1, newRequestTime]}
else:
if userAgent not in ipDict[ipAddr]:
ipDict[ipAddr][userAgent] = [1, newRequestTime]
else:
ipdipaua = ipDict[ipAddr][userAgent]
if newRequestTime - ipdipaua[1] >= sessionTimeout:
ipdipaua[0] += 1
ipdipaua[1] = newRequestTime
infile.close()
return recordsRead
def outputSessions():
outfile = open(outfileName, "w")
outfile.write("#Fields: IPAddr Sessions\n")
recordsWritten = len(ipDict)
# ipDict[ip] is { userAgent1: [numSessions, lastTimeStamp], ... }
for ip, val in ipDict.iteritems():
# TODO: sum over on all keys' values [(v, k) for (k, v) in d.iteritems()].
totalSessions = reduce(operator.add, [v2[0] for v2 in val.itervalues()])
outfile.write("%s\t%d\n" % (ip, totalSessions))
outfile.close()
return recordsWritten
recordsRead = inputRecords()
recordsWritten = outputSessions()
print "Finished session reconstruction: read %d records, wrote %d\n" % (recordsRead, recordsWritten)
Update: This took 39 seconds to input and process 342K records and write 21K
records. That's good enough speed for my purposes. Apparently 3/4 of that time
was spent in `strptime()`!
|
Making all variables in a scope global or importing a module inside another module
Question: I have a package with two modules in it. One is the `__init__` file, and the
other is a separate part of the package. If I try `from mypackage import
separatepart`, the code in the `__init__` module is run, which will run
unneeded code, slowing down the importing by a lot. The code in separate part
won't cause any errors, and so users should be able to directly import it
without importing the `__init__` module.
Since I can't figure out a way to do this, I thought I should include a
function in the `__init__` file that does everything so nothing would be done
directly, but in order to do this, I would need to have any variables set to
be global. Is there any way to tell Python that all variables are global in a
function, or to not run the `__init__` module?
Answer: dthat I know of, there is not way to specify that _all_ variables are global
but you can import the module while you are in the module.~~just make sure
that you do it in a function that isn't called at the top level, you are
playing with infinite recursion here but a simple use should be safe.~~
#module.py
foo = bar = 0 # global
def init()
import module as m
m.foo = 1
m.bar = 2 # access to globals
~~if`init` was called at the top level, then you have infinite recursion but
it sounds like the whole point of this is to avoid this code running at the
top level, so you should be safe.~~ Since you want to do this in the
`__init__.py` file, just import the top level of the package.
It occurred to me on a walk that there's no problem with recursion here
because the top level code will only run once on initial import.
|
How can I replace the class by monkey patching?
Question: How can I replace the ORM class - so it should not cause recursion !!!
_Problem_ :
original class has the super call, when its got replaced - it causes self
inheritance and causes maximum recursion depth exceed exception.
i.e. class orm is calling super(orm, self).... and orm has been replaced by
another class which inherits original orm....
# Package !
addons __init__.py osv run_app.py
./addons:
__init__.py test_app1.py test.py
./osv:
__init__.py orm.py
# contents of orm.py
class orm_template(object):
def __init__(self, *args, **kw):
super(orm_template, self).__init__()
def fields_get(self, fields):
return fields
def browse(self, id):
return id
class orm(orm_template):
def __init__(self, *args, **kw):
super(orm, self).__init__(*args, **kw)
def fields_get(self, fields, context = None):
return super(orm, self).fields_get(fields)
def read(self, fields):
return fields
# contents of addons/**init**.py
import test
def main(app):
print "Running..."
__import__(app, globals(), locals())
# contents of addons/test.py
from osv import orm
import osv
class orm(orm.orm):
def __init__(self, *args, **kw):
super(orm, self).__init__(*args, **kw)
def fields_get(self, *args, **kw):
print "my fields get................."
return super(orm, self).fields_get(*args, **kw)
osv.orm.orm = orm
print "replaced.........................."
# contents of test_app1.py
from osv.orm import orm
class hello(orm):
_name = 'hellos'
def __init__(self, *args, **kw):
super(hello, self).__init__(*args, **kw)
print hello('test').fields_get(['name'])
# contents of run_app.py
import addons
addons.main('test_app1')
### OUTPUT
>>>python run_app.py
replaced..........................
Running...
...
...
super(orm, self).__init__(*args, **kw)
RuntimeError: maximum recursion depth exceeded
I've seen the similar
[question](http://stackoverflow.com/questions/3765222/monkey-patch-python-
class)
Answer: Your `addons/test.py` needs to get and keep a reference to the original
`orm.orm` and use that instead of the replaced version. I.e.:
from osv import orm
import osv
original_orm = osv.orm
class orm(original_orm):
def __init__(self, *args, **kw):
super(orm, self).__init__(*args, **kw)
def fields_get(self, *args, **kw):
print "my fields get................."
return super(orm, self).fields_get(*args, **kw)
osv.orm.orm = orm
print "replaced.........................."
so the monkeypatched-in class inherit from the original rather than from
itself, as you had it in your setup. BTW, if you can avoid monkey-patching by
better design of the `osv` module (e.g. w/a setter function to set what's the
orm) you'll be happier;-).
|
How to submit web forms using Python?
Question: First of all, sorry if this question is a little vague and rambling! I'm ok
with Python, but I've never done anything HTTP related before.
I'm trying to automate submitting a web form, and from reading some of [this
page](http://www.jmarshall.com/easy/http/) I understand that I need to do a
POST request. I also found a code snippet demonstrating the urllib module:
import urllib
params = urllib.urlencode({'spam': 1, 'eggs': 2, 'bacon': 0})
f = urllib.urlopen("http://www.musi-cal.com/cgi-bin/query", params)
print f.read()
But I still don't really understand what I'm doing. I need to trigger "submit"
somehow, and I assume the actual data I'm submitting will go in the params
somewhere?
Answer: The code there should do what you want.
Whatever data you want to use should go into the params as you have in your
example. When the params are included as an argument to urlopen a POST request
will be used (instead of a GET).
By just calling urlopen I believe the POST request will be submitted. If you
want the response however you will need to use f.read().
|
how to read password protected excel in python
Question: I'm new to python programming, and I am trying to read a password protected
file using python, the code is shown below:
import sys
import win32com.client
xlApp = win32com.client.Dispatch("Excel.Application")
print "Excel library version:", xlApp.Version
filename,password = 'C:\myfiles\foo.xls', 'qwerty12'
xlwb = xlApp.Workbooks.Open(filename, Password=password)
But then the xls file is loaded but still prompt me to provide the password, I
can't let python to enter the password for me.
What have I done wrong? Thanks!
Answer: Open takes two types of password, namely:
Password: password required to open a protected workbook.
WriteResPassword : password required to write to a write-reserved workbook
So in your case , is it write protected or protection on open?
Also there is a discussion on SO that says that this does not work with named
parameters, So try providing all parameter values with the defaults
* <http://stackoverflow.com/questions/2887339/how-to-open-write-reserved-excel-file-in-python-with-win32com>
Default values are documented in MSDN
* <http://msdn.microsoft.com/en-us/library/microsoft.office.interop.excel.workbooks.open.aspx>
|
get rhythmbox information from other user
Question: I have Rhythmbox running on my desktop, and I want to be able to control it
from remotely via a web interface. I'm having problems accessing it, however,
because `rhythmbox-client` is complaining that the user (www-data) that is
trying to access it doesn't a) have as X session running, and b) doesn't have
access to my rhythmbox dbus information.
`(rhythmbox-client:13954): Rhythmbox-WARNING **: /bin/dbus-launch terminated
abnormally with the following error: Autolaunch error: X11 initialization
failed.`
I'm running apache, php on ubuntu 10.04. The following methods have also been
tried by calling the php script via php cli from a different user (sshing into
my own box with a different user)
I've tried these approaches:
* calling system() and exec() from the php script with "rhythmbox-client --print-playing --no-start --no-resent"
* using DBus directly in php as well as a python script (calling it from the php script with system()/exec())
* using `setuid()`, `setruid()`, `seteuid()` in a C program and calling it via php.
I'm at a loss now. Is this even possible?
[EDIT] I have used @IvanGoneKrazy's suggestion and taken the environ code from
[this similar question](http://stackoverflow.com/questions/2143785/python-
dbus-session-bus-x11-dependency). Now I have this code with this error
message:
import subprocess, os
p = subprocess.Popen('dbus-launch', shell=True, stdout=subprocess.PIPE, stderr=subprocess.STDOUT)
for var in p.stdout:
sp = var.split('=', 1)
os.environ[sp[0]] = sp[1][:-1]
os.system('rhythmbox-client --print-playing')
error message:
(rhythmbox-client:15377): Rhythmbox-WARNING **: Launch helper exited with unknown return code 1
Answer: A similar problem and Python solution for is given
[here](http://stackoverflow.com/questions/2143785/python-dbus-session-
bus-x11-dependency). The root issue seems to be that system() and exec() do
not have the correct environment variables set. You can use PHPs
<http://us.php.net/manual/en/function.proc-open.php> to set the environment
vars for your PHP spawned process.
|
How to check if a word is an English word with Python?
Question: I want to check in a Python program if a word is in the English dictionary.
I believe nltk wordnet interface might be the way to go but I have no clue how
to use it for such a simple task.
def is_english_word(word):
pass # how to I implement is_english_word?
is_english_word(token.lower())
In the future, I might want to check if the singular form of a word is in the
dictionary (e.g., properties -> property -> english word). How would I achieve
that?
Answer: For (much) more power and flexibility, use a dedicated spellchecking library
like [`PyEnchant`](http://pythonhosted.org/pyenchant/). There's a
[tutorial](http://pythonhosted.org/pyenchant/tutorial.html), or you could just
dive straight in:
>>> import enchant
>>> d = enchant.Dict("en_US")
>>> d.check("Hello")
True
>>> d.check("Helo")
False
>>> d.suggest("Helo")
['He lo', 'He-lo', 'Hello', 'Helot', 'Help', 'Halo', 'Hell', 'Held', 'Helm', 'Hero', "He'll"]
>>>
`PyEnchant` comes with a few dictionaries (en_GB, en_US, de_DE, fr_FR), but
can use any of the [OpenOffice
ones](http://wiki.services.openoffice.org/wiki/Dictionaries) if you want more
languages.
There appears to be a pluralisation library called
[`inflect`](http://pypi.python.org/pypi/inflect), but I've no idea whether
it's any good.
|
How to open SQL Compact database read only
Question: There is a SQL Compact v3.1 database that I want to quickly read. I'm doing
this in python so I don't have access to managed code.
I've noticed that if I use adodbapi the database file actually gets modified
just by opening it. And sadly when I add 'File mode=Read Only' to the
connection string I get a weird error.
Here is the code I use to connect:
import adodbapi
adodbapi.connect('Provider=Microsoft.SQLSERVER.MOBILE.OLEDB.3.0; Data Source="awesome.sdf"; File mode = Read Only;SSCE:Temp File Directory=c:\temp\\;')
And then I get the error message
OperationalError: (com_error(-2147352567, 'Exception occurred.', (0, u'Microsoft OLE DB Service Components',
u'Multiple-step OLE DB operation generated errors. Check each OLE DB status value, if available. No work was done.',
None, 0, -2147217887), None),
u'Error opening connection: Provider=Microsoft.SQLSERVER.MOBILE.OLEDB.3.0; Data Source="Awesome.sdf";File mode = Read Only;SSCE:Temp File Directory="c:\\\temp\\";')
I added the SSCE because when I wrote a test program in C# it needed it. The
following code works perfectly fine and doesn't modify the file when you do a
simple SELECT query.
conn = new SqlCeConnection("Data Source = awesome.spf; File mode = Read Only;SSCE:Temp File Directory=\"c:\\users\\evelio\\desktop\\\";");
conn.Open();
Thanks for the help,
Evelio
Answer: Look here: <http://social.msdn.microsoft.com/Forums/en-
US/sqlce/thread/bf70c615-b279-4a91-b964-0ff99adc7ab8/#674f6a79-a3b4-4601-a952-860a7e8f3169>
cn.Mode = adModeRead
|
How can you select a random element from a list, and have it be removed?
Question: Let's say I have a list of colours, `colours = ['red', 'blue', 'green',
'purple']`.
I then wish to call this python function that I hope exists, `random_object =
random_choice(colours)`. Now, if random_object holds 'blue', I hope `colours =
['red', 'green', 'purple']`.
Does such a function exist in python?
Answer: Firstly, if you want it removed because you want to do this again and again,
you might want to use `random.shuffle()` in the random module.
`random.choice()` picks one, but does not remove it.
Otherwise, try:
import random
# this will choose one and remove it
def choose_and_remove( items ):
# pick an item index
if items:
index = random.randrange( len(items) )
return items.pop(index)
# nothing left!
return None
|
Mapping Languages to Paradigms
Question: I recently read Eric Steven Raymond's article "How To Become A Hacker" and I
like his suggestion of learning 5 key languages (he suggests Python, C/C++,
Lisp, Java, and Perl) as a way of covering the main programming paradigms in
use today.
His advice is that it's not so important which specific languages a programmer
knows. It's more important to know different approaches to programming, for
two reasons.
The first reason is that it makes it trivial to pick up a new language, once
you know the general approach to the way it solves problems.
The second reason is that there is no one best language - they all have trade-
offs. It would be best to know what type of language to pick given a specific
type of problem. This is what I'm most interested in, but I'm having a problem
really distinguishing between the 5 languages he suggests. There seems to be a
lot of overlap.
So my specific question is, given these 5 languages, what is their intended
programming paradigm, and give one example of the type of problem it would be
best suited for.
An example answer (and I'm not sure this answer is correct):
Perl
- mainly a functional language
- great for quick text substitutions in multiple files from the command line.
I found a few other similar questions posted, but I'd like to know about these
5 languages in particular. I'm just looking for a starting point, nothing too
detailed. Thanks in advance!
Answer: I think you're approaching it wrong. As esr himself says, it's not the
_language_ that matters, it's the _paradigm_. So when you say that
> 1. Perl is a functional language
> 2. It's great for quick text substitutions in multiple files from the
> command line
>
you are missing one of the main points of a functional language which is that
they are great for building large systems using a bottom up approach: solve a
bunch of (well chosen) small problems with well designed functions until we
have a complete system. We cut down on code duplication by identifying what
algorithms that we are using have in common and using higher order functions
to encapsulate their commonality. We minimize (overt) branching behavior by
using higher order functions to cook up just the function that we need for a
given situation.
Likewise, I could say that
> 1. Java is mainly an OOP language
> 2. It's good for writing large, robust systems,
>
but that misses the point that OOP languages are about modeling concepts from
the problem domain in code so that we are left with a clear way to
imperatively solve the problem at hand. We cut down on code duplication by
identifying what the relevant concepts have in common and encapsulating the
code that deals with those commonalities in a class that describes it. We
minimize (overt) branching behavior by providing different subclasses of an
abstraction with appropriately different behavior.
On the whole, the basic point of programming languages and their associated
paradigms is
* to allow you to not think about anything that doesn't affect the quality of the resulting program. If that wasn't a (largely) desirable thing, then we would all be writing machine code.
* This is accomplished by (among other things) providing a set of tools for _building abstractions_.
Shop around and pick one that you like and get good at. Just make sure that
you learn when the other ones allow for a better solution (this will probably
mean getting good at them eventually too ;). I think that you can mainly take
"good solution" to mean, "clear mapping of **code** to **ideas** ". (modulo
concerns about efficiency that would force you (provide an excuse?) to write
in a language like C)
|
python mechanize javascript submit button problem!
Question: im making some script with mechanize.browser module.
one of problem is all other thing is ok, but when submit() form,it not
working,
so i was found some suspicion source part.
in the html source i was found such like following.
im thinking, loginCheck(this) making problem when submit form.
but how to handle this kind of javascript function with mechanize module ,so i
can
successfully submit form and can receive result?
following is websource snippet which related with loginCheck(this) javascript
function.
function init(){
FRMLOGIN.ID.focus();
}
function loginCheck(f){
if(chkNull(f.ID, "아이디를"))
return false;
if(chkNull(f.PWD, "패스워드를"))
return false;
//f.target = "ifrmLoginHidden";
f.action = (f.SECCHK.checked) ? "https://user.buddybuddy.co.kr/Login/Login.asp" : "http://user.buddybuddy.co.kr/Login/Login.asp";
}
i know mechanize not support javascript, so i want to make progammatically
loginCheck()
function with python mechanize code.
anyone would you some help me to make this javascript function to python
mechanize
translated code?
so correctly can login with website?
if so much appreciate!
# -*- coding: cp949-*-
import sys,os
import mechanize, urllib
import cookielib
from BeautifulSoup import BeautifulSoup,BeautifulStoneSoup,Tag
import datetime, time, socket
import re,sys,os,mechanize,urllib,time
br = mechanize.Browser()
cj = cookielib.LWPCookieJar()
br.set_cookiejar(cj)
# Browser options
br.set_handle_equiv(True)
br.set_handle_gzip(True)
br.set_handle_redirect(True)
br.set_handle_referer(True)
br.set_handle_robots(False)
# Follows refresh 0 but not hangs on refresh > 0
br.set_handle_refresh(mechanize._http.HTTPRefreshProcessor(), max_time=1)
# Want debugging messages?
br.set_debug_http(True)
br.set_debug_redirects(True)
br.set_debug_responses(True)
# User-Agent (this is cheating, ok?)
br.addheaders = [('User-agent', 'Mozilla/5.0 (Windows; U; Windows NT 6.0; en-US; rv:1.9.0.6')]
br.open('http://user.buddybuddy.co.kr/Login/LoginForm.asp?URL=')
html = br.response().read()
print html
br.select_form(name='FRMLOGIN')
print br.viewing_html()
br.form['ID']='psh7943'
br.form['PWD']='qkrthgus'
br.submit()
print br.response().read()
if anyone can help me ..much appreciate!!
Answer: You can go through the login process by hand in your browser and check (using
e.g. Firebug in firefox, Developer Tools in Chrome etc.) what requests are
sent to the site when you hit the OK button. Usually this is a POST request
with data taken from the login form. Check what data are sent in this request
and execute your own post request with:
mechanize.urlopen(URL, POST_DATA).
You can extract POST_DATA (and post_url) from mechanize's form object using:
form.click_request_data()
but you may need to do some modifications.
Very simple example:
br.select_form(name='form_name')
br.form['login']='login'
br.form['pass']='pass'
post_url, post_data, headers = br.form.click_request_data()
mechanize.urlopen(post_url, post_data)
|
permissive equality test on string
Question: I'm a python newbie with a problem too hard to tackle.
I have a string defining a path, were all the spaces have been converted to
underscores. How can I find if it corresponds to a real path?
e.g. a string like `/some/path_to/directory_1/and_to/directory_2`
with a real path: `/some/path_to/directory 1/and_to/directory 2`
notice that the real path can contain BOTH spaces and underscores.
How can I feed it to `os.path.exists()` ???
thanks alessandro
Answer: Use [glob](http://docs.python.org/library/glob.html) but replacing every
underscore with a range `[ _]`:
import glob
glob.glob('/some/path_to/directory_1/and_to/directory_2'.replace('_', '[ _]'))
Note that this will fail if your path contains the character `[`. You can fix
this by first replacing `[` with `[[]`.
|
uploading records of list of files in parallel using python to DB
Question: I have a list of files each file have mass of records separting by \n , i need
to proccess those records in parallel and upload them to some sql server could
someone provide an idea what is the best way to do this with python
Answer: The best way might not be to upload in parallell but use SQL Servers bulk
importing mechanisims
e.g.
[BULK INSERT](http://msdn.microsoft.com/en-us/library/ms188365.aspx)
[bcp](http://msdn.microsoft.com/en-us/library/ms162802.aspx)
EDIT:
If you need to process them then a way I have often used is
1) bulk load the data into a staging table
2) Process the data on the database
3) Insert into main tables
Stages 2 and 3 can be combined if the processing is of a reasonable type.
This could be faster as there are less round trips to the server and
processing a set of data rather than row by row is usually quicker.
Also I thing that SQL server will make use of more than one CPU in doing this
processing so you get your processing parallel for free
|
IOError: request data read error
Question: I seem to be getting an IOError: request data read error quite a lot when i'm
doing an Ajax upload. For example out of every 5 file uploads it errors out on
atleast 3.
Other people seem to have had the same issue. Eg.
* <http://stackoverflow.com/questions/2641665/django-upload-failing-on-request-data-read-error>
* <http://stackoverflow.com/questions/411902/django-file-upload-failing-occasionally>
Some other observations:
* It's definitely not my internet connection or a browser issue. Seems to be happening on all browsers chrome/FF/opera.
* I'm running **django 1.1.1 Apache/2.2.14 (Ubuntu) mod_ssl/2.2.14 OpenSSL/0.9.8k mod_wsgi/2.8 Python/2.6.5** on Lucid.
* It is also not the file size. I can sometimes upload 1+ MB files but fail on 180 Kb files.
* * *
**Traceback**
Traceback (most recent call last):
File "/home/ubuntu/.virtualenvs/anonymous_app/lib/python2.6/site-packages/django/core/handlers/base.py", line 98, in get_response
response = middleware_method(request, e)
File "/home/ubuntu/.virtualenvs/anonymous_app/lib/python2.6/site-packages/django/core/handlers/base.py", line 92, in get_response
response = callback(request, *callback_args, **callback_kwargs)
File "/home/ubuntu/.virtualenvs/anonymous_app/lib/python2.6/site-packages/django/contrib/auth/decorators.py", line 78, in __call__
return self.view_func(request, *args, **kwargs)
File "/home/ubuntu/webapps/anonymous_app/app/do_work/views/__init__.py", line 391, in some_form_ajax_upload
f = request.FILES.get('file_upload')
File "/home/ubuntu/.virtualenvs/anonymous_app/lib/python2.6/site-packages/django/core/handlers/wsgi.py", line 187, in _get_files
self._load_post_and_files()
File "/home/ubuntu/.virtualenvs/anonymous_app/lib/python2.6/site-packages/django/core/handlers/wsgi.py", line 137, in _load_post_and_files
self._post, self._files = self.parse_file_upload(self.META, self.environ['wsgi.input'])
File "/home/ubuntu/.virtualenvs/anonymous_app/lib/python2.6/site-packages/django/http/__init__.py", line 124, in parse_file_upload
return parser.parse()
File "/home/ubuntu/.virtualenvs/anonymous_app/lib/python2.6/site-packages/django/http/multipartparser.py", line 133, in parse
for item_type, meta_data, field_stream in Parser(stream, self._boundary):
File "/home/ubuntu/.virtualenvs/anonymous_app/lib/python2.6/site-packages/django/http/multipartparser.py", line 606, in __iter__
for sub_stream in boundarystream:
File "/home/ubuntu/.virtualenvs/anonymous_app/lib/python2.6/site-packages/django/http/multipartparser.py", line 420, in next
return LazyStream(BoundaryIter(self._stream, self._boundary))
File "/home/ubuntu/.virtualenvs/anonymous_app/lib/python2.6/site-packages/django/http/multipartparser.py", line 446, in __init__
unused_char = self._stream.read(1)
File "/home/ubuntu/.virtualenvs/anonymous_app/lib/python2.6/site-packages/django/http/multipartparser.py", line 299, in read
out = ''.join(parts())
File "/home/ubuntu/.virtualenvs/anonymous_app/lib/python2.6/site-packages/django/http/multipartparser.py", line 292, in parts
chunk = self.next()
File "/home/ubuntu/.virtualenvs/anonymous_app/lib/python2.6/site-packages/django/http/multipartparser.py", line 314, in next
output = self._producer.next()
File "/home/ubuntu/.virtualenvs/anonymous_app/lib/python2.6/site-packages/django/http/multipartparser.py", line 375, in next
data = self.flo.read(self.chunk_size)
File "/home/ubuntu/.virtualenvs/anonymous_app/lib/python2.6/site-packages/django/http/multipartparser.py", line 405, in read
return self._file.read(num_bytes)
IOError: request data read error
<WSGIRequest
GET:<QueryDict: {}>,
POST:<could not parse>,
COOKIES:{'__utma': '168279989.1688771210.1285773436.1285773436.1285773436.1',
'__utmb': '168279989.20.10.1285773436',
'__utmc': '168279989',
'__utmz': '168279989.1285773436.1.1.utmcsr=(direct)|utmccn=(direct)|utmcmd=(none)',
'beta': 'True',
'sessionid': 'b1ecf92f2bba13e1885d07803e10aa03',
'timezone_offset': '-330'},
META:{'CONTENT_LENGTH': '188575',
'CONTENT_TYPE': 'multipart/form-data; boundary=---------------------------57602381214905740261171925981',
'DOCUMENT_ROOT': '/htdocs',
'GATEWAY_INTERFACE': 'CGI/1.1',
'HTTPS': '1',
'HTTP_ACCEPT': 'text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8',
'HTTP_ACCEPT_CHARSET': 'ISO-8859-1,utf-8;q=0.7,*;q=0.7',
'HTTP_ACCEPT_ENCODING': 'gzip,deflate',
'HTTP_ACCEPT_LANGUAGE': 'en-us,en;q=0.5',
'HTTP_CONNECTION': 'keep-alive',
'HTTP_COOKIE': 'beta=True; __utma=168279989.1688771210.1285773436.1285773436.1285773436.1; __utmb=168279989.20.10.1285773436; __utmc=168279989; __utmz=168279989.1285773436.1.1.utmcsr=(direct)|utmccn=(direct)|utmcmd=(none); sessionid=b1ecf92f2bba13e1885d07803e10aa03; timezone_offset=-330',
'HTTP_HOST': 'xxxxxx.compute-1.amazonaws.com',
'HTTP_KEEP_ALIVE': '115',
'HTTP_REFERER': 'https://ec2-184-72-79-96.compute-1.amazonaws.com/do-my-somees/enter/some-documents/',
'HTTP_USER_AGENT': 'Mozilla/5.0 (X11; U; Linux i686; en-US; rv:1.9.2.10) Gecko/20100915 Ubuntu/10.04 (lucid) Firefox/3.6.10',
'PATH': '/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin:/usr/X11R6/bin',
'PATH_INFO': u'/do-my-somees/enter/some-documents/ajax-upload/Other-some-Document/',
'PATH_TRANSLATED': '/home/ubuntu/webapps/anonymous_app/settings/apache/qa.wsgi.py/do-my-somees/enter/some-documents/ajax-upload/Other-some-Document/',
'QUERY_STRING': '',
'REMOTE_ADDR': '',
'REMOTE_PORT': '15561',
'REQUEST_METHOD': 'POST',
'REQUEST_URI': '/do-my-somees/enter/some-documents/ajax-upload/Other-some-Document/',
'SCRIPT_FILENAME': '/home/ubuntu/webapps/anonymous_app/settings/apache/qa.wsgi.py',
'SCRIPT_NAME': u'',
'SERVER_ADDR': '10.196.142.182',
'SERVER_ADMIN': 'dev@anonymous_app.com',
'SERVER_NAME': 'ec2-184-72-79-96.compute-1.amazonaws.com',
'SERVER_PORT': '443',
'SERVER_PROTOCOL': 'HTTP/1.1',
'SERVER_SIGNATURE': '<address>Apache/2.2.14 (Ubuntu) Server at ec2-184-72-79-96.compute-1.amazonaws.com Port 443</address>\n',
'SERVER_SOFTWARE': 'Apache/2.2.14 (Ubuntu)',
'SSL_TLS_SNI': 'ec2-184-72-79-96.compute-1.amazonaws.com',
'mod_wsgi.application_group': 'qa.anonymous_app.com|',
'mod_wsgi.callable_object': 'application',
'mod_wsgi.listener_host': '',
'mod_wsgi.listener_port': '443',
'mod_wsgi.process_group': '',
'mod_wsgi.reload_mechanism': '0',
'mod_wsgi.script_reloading': '1',
'mod_wsgi.version': (2, 8),
'wsgi.errors': <mod_wsgi.Log object at 0xb9456860>,
'wsgi.file_wrapper': <built-in method file_wrapper of mod_wsgi.Adapter object at 0xb936a968>,
'wsgi.input': <mod_wsgi.Input object at 0xb9720e30>,
'wsgi.multiprocess': True,
'wsgi.multithread': False,
'wsgi.run_once': False,
'wsgi.url_scheme': 'https',
'wsgi.version': (1, 0)}>
Answer: I get this exception, too. In the Apache error logfile I see this:
[Wed Aug 17 08:30:45 2011] [error] [client 10.114.48.206] (70014)End of file found: mod_wsgi (pid=9722): Unable to get bucket brigade for request., referer: https://egs-work/modwork/beleg/188074/edit/
[Wed Aug 17 08:30:45 2011] [error] [client 10.114.48.206] mod_wsgi (pid=3572): Exception occurred processing WSGI script '/home/modwork_egs_p/modwork_egs/apache/django_wsgi.py'.
[Wed Aug 17 08:30:45 2011] [error] [client 10.114.48.206] IOError: failed to write data
Versions:
apache2-prefork-2.2.15-3.7.x86_64
apache2-mod_wsgi-3.3-1.8.x86_64 WSGIDaemonProcess with threads=1
mod_ssl/2.2.15
Linux egs-work 2.6.34.8-0.2-default #1 SMP 2011-04-06 18:11:26 +0200 x86_64 x86_64 x86_64 GNU/Linux
openSUSE 11.3 (x86_64)
First I was confused, because the last line "failed to **write** data" does
not fit to the django code "load post data". But I guess that django wants to
write an error page to the client. But the client has canceled the tcp
connection. And now http 500 page can't be written to the client.
The client disconnected after sending the request, and before getting the
response:
* The user closed the browser or navigated to an other page.
* The user pressed the reload button.
I have seen this only with POST-Requests (not GET). If POST is used, the
webserver does read at least twice: First to get the headers, the second to
get the data. The second read fails.
It is easy to reproduce:
Insert some code which waits before the first access to request.POST happens
(be sure, that no middleware accesses request.POST before time.sleep()):
def edit(request):
import time
time.sleep(3)
#.....
Now do a big POST (e.g. file upload). I don't know the apache buffer size. But
5 MB should be enough. When the browser shows the hourglass, browse to an
other page. The browser will cancel the request and the exception should be in
the logfile.
This is my Middleware, since I don't want to get the above traceback in our
logfiles:
class HandleExceptionMiddleware:
def process_exception(self, request, exception):
if isinstance(exception, IOError) and 'request data read error' in unicode(exception):
logging.info('%s %s: %s: Request was canceled by the client.' % (
request.build_absolute_uri(), request.user, exception))
return HttpResponseServerError()
|
More pythonic way to write this?
Question: I have this code here:
import re
def get_attr(str, attr):
m = re.search(attr + r'=(\w+)', str)
return None if not m else m.group(1)
str = 'type=greeting hello=world'
print get_attr(str, 'type') # greeting
print get_attr(str, 'hello') # world
print get_attr(str, 'attr') # None
Which works, but I am not particularly fond of this line:
return None if not m else m.group(1)
In my opinion this would look cleaner if we could use a ternary operator:
return (m ? m.group(1) : None)
But that of course isn't there. What do you suggest?
Answer: Python _has_ a ternary operator. You're using it. It's just in the `X if Y
else Z` form.
That said, I'm prone to writing these things out. Fitting things on one line
isn't so great if you sacrifice clarity.
def get_attr(str, attr):
m = re.search(attr + r'=(\w+)', str)
if m:
return m.group(1)
return None
|
Python and C interaction - callback function
Question: I'm trying to make a key logger for Mac OS for one of my research projects. I
have a C code which will grab keystroke and write them to a text file. (The
following code I have taken out some not important stuff)
What I need to do now is just like PyHook, instead of write the data to a text
file, to pass a Python callback function to the C code and make it passes back
the key input to Python, so I can do necessary analysis with Python.
I have look for how to do it, but honestly I have no idea how to approach
this, as I am not used to C programming or Python extensions. Any help would
be greatly appreciated.
#include <Carbon/Carbon.h>
#include <ApplicationServices/ApplicationServices.h>
#include <unistd.h>
#include <stdio.h>
#include <sys/time.h>
#define NUM_RECORDING_EVENT_TYPES 5
#define RECORD 0
#define MOUSEACTION 0
#define KEYSTROKE 1
// maximum expected line length, for fgets
#define LINE_LENGTH 80
#define kShowMouse TRUE
OSStatus RUIRecordingEventOccurred(EventHandlerCallRef nextHandler, EventRef theEvent, void *userData);
void prepareToRecord(); // install the event handler, wait for record signal
// note that keyboard character codes are found in Figure C2 of the document
// Inside Macintosh: Text available from http://developer.apple.com
char * keyStringForKeyCode(int keyCode); // get the representation of the Mac keycode
// Global Variables
int dieNow = 0; // should the program terminate
int ifexit = 0; // Exit state
char *filename = NULL; // Log file name
FILE *fd = NULL; // Log file descriptor
int typecount = 0; // count keystroke to periodically save to a txt file
struct timeval thetime; // for gettimeofday
long currenttime; // the current time in milliseconds
int main()
{
filename = "test.txt";
fd = fopen(filename, "a");
// Get RUI ready to record or play, based off of mode
prepareToRecord();
return EXIT_SUCCESS;
}
// event handler for RUI recorder
OSStatus RUIRecordingEventOccurred(EventHandlerCallRef nextHandler, EventRef theEvent, void *userData)
{
// Determine class and kind of event
int eventClass = GetEventClass(theEvent);
int eventKind = GetEventKind(theEvent);
/* Handle Keyboard Events */
if((eventClass == kEventClassKeyboard) && (eventKind == kEventRawKeyDown)) /* key release implied */ {
int keyCode, modifiers; // what did the user press? any modifier keys down?
// gather keystroke information
GetEventParameter(theEvent, kEventParamKeyCode, typeInteger, NULL, sizeof(keyCode), NULL, &keyCode);
GetEventParameter(theEvent, kEventParamKeyModifiers, typeInteger, NULL, sizeof(modifiers), NULL, &modifiers);
// What time is it?
gettimeofday(&thetime, NULL);
currenttime =(((thetime.tv_sec*1000000) + (thetime.tv_usec)));
fprintf(fd, "%s\n", keyStringForKeyCode(keyCode));
}
return EXIT_SUCCESS;
}
void prepareToRecord()
{
EventRecord event; // holds an event for examination
// Types of events to listen for
EventTypeSpec eventTypes[NUM_RECORDING_EVENT_TYPES] = {{kEventClassKeyboard, kEventRawKeyDown}};
// Install the event handler
InstallEventHandler(GetEventMonitorTarget(), NewEventHandlerUPP(RUIRecordingEventOccurred), NUM_RECORDING_EVENT_TYPES, eventTypes, nil, nil);
// event loop - get events until die command
do {
WaitNextEvent((everyEvent),&event,GetCaretTime(),nil);
} while (dieNow == 0);
}
char * keyStringForKeyCode(int keyCode)
{
// return key char
switch (keyCode) {
case 0: return("a");
default: return("Empty"); // Unknown key, Return "Empty"
}
}
Answer: It's easy - Just Follow the instructions - [Calling Python Functions from
C](http://docs.python.org/release/2.5.2/ext/callingPython.html).
Alternatively if you are trying to call C/C++ functions from Python you can
use [SWIG](http://www.swig.org/) or one of Python's module
[CTypes](http://docs.python.org/library/ctypes.html)
|
Best way to change the value of "settings" from within a Python test case?
Question: I'm writing unit tests in Python for the first time, for a Django app. I've
struck a problem. In order to test a particular piece of functionality, I need
to change the value of one of the app's settings. Here's my first attempt:
def test_in_list(self):
mango.settings.META_LISTS = ('tags',)
tags = Document(filepath).meta['tags']
self.assertEqual(tags, [u'Markdown', u'Django', u'Mango'])
What I'm trying to do is change the value of `META_LISTS` such that the new
value is used when the `Document` object is created. The relevant imports
are...
# tests.py
from mango.models import Document
import mango.settings
# models.py
from mango.settings import *
If I've understood correctly, since `models.py` has already imported the names
from `mango.settings`, changing the value of `META_LISTS` within
`mango.settings` will not alter the value of `META_LISTS` within
`mango.models`.
It's possible – likely even – that I'm going about this in completely the
wrong way. What's the correct way to alter the value of such a "setting" from
within a test case?
**Edit:** I failed to mention that the file `models.py` contains vanilla
Python classes rather than Django models. I certainly need to rename this
file!
Answer: In models.py, use `import mango.settings`. You can then set a variable in your
test code like you would any other:
mango.settings.foo = 'bar'
A module is a singleton. You can change the values in its namespace from
anywhere in your code.
But this won't work if you use `from mango.settings import *`, since that
expression copies the values in the module into the current namespace.
|
dynamic values in kwargs
Question: I have a layer which helps me populating records from the form to tables and
viceversa, it does some input checking, etc.
Now several methods of this layer which are called several times in different
parts of the webform take the same parameters, so I wanted to pack them at the
begining of the codefile.
> kwargs(): return {"tabla":"nombre_tabla","id":[hf_id.Value] ,"container":
> Panel1,"MsgBox1": MsgBox1}
then I call
> IA.search(**kwargs)
but doing that way the values of the dictionary get fixed with the ones they
had in the begining, and one of them is retrieved from a webcontrol so it
needs to be dynamic. So I wrapped them in a function
> def kwargs(): return {"tabla":"nombre_tabla", "id":[hf_id.Value]
> ,"container": Panel1,"MsgBox1": MsgBox1}
and then I call
> IA.search(*_kwargs()) IA.save(_ *kwargs())
etc.
and that way the value of the dictionary which comes from the webform (hf_id)
is dynamic and not fixed. But I was wondering if in this case there is another
way, a pythonic way, to get the values of the dictionary kwargs to be dynamic
and not fixed
Answer: Python objects are pointers (though they are not directly manipulatable by the
user.)
So if you create a list like this:
>>> a = [1, 2, 3]
and then store it in a dictionary:
>>> b = { 'key': a, 'anotherkey': 'spam' }
you will find modifications to the value in the dictionary also modify the
original list:
>>> b['key'].append(4)
>>> print b['key']
[1, 2, 3, 4]
>>> print a
[1, 2, 3, 4]
If you want a copy of an item, so that modifications will not change the
original item, then use the copy module.
>>> from copy import copy
>>> a = [1, 2, 3]
>>> b['key'] = copy(a)
>>> print b['key']
[1, 2, 3]
>>> b['key'].append(4)
>>> print b['key']
[1, 2, 3, 4]
>>> print a
[1, 2, 3]
|
Python, using subprocess.Popen to make linux command line call? I'm getting "[Errno 2] No such file or directory"
Question: I'm trying to follow the info I can find about subprocess.Popen as I want to
make a linux command line call.. I am trying as below but am getting the error
"[Errno 2] No such file or directory". I'm not trying to open a file so I
don't understand this error, and it works fine (although with other issues
relating to waiting for the process to finish when I don't want it to) when I
use a regular os.popen.
I can't seem to figure out how to do this properly, any advice is appreciated.
EDIT: THE COMMAND I AM USING IS COMPLEX AND VARIABLIZED, it would be too out-
of-context to include it here, I think its suffice to say that the code works
when I use `os.popen` and not when I do the new way, so no, the "linux command
line call" is obviously not the call I am using
subprocess.Popen([r"linux command line call"])
>>> [Errno 2] No such file or directory
Answer:
import subprocess
proc=subprocess.Popen(['ls','-l']) # <-- Change the command here
proc.communicate()
`Popen` expects a list of strings. The first string is typically the program
to be run, followed by its arguments. Sometimes when the command is
complicated, it's convenient to use `shlex.split` to compose the list for you:
import shlex
proc=subprocess.Popen(shlex.split('ls -l'))
proc.communicate()
|
Extension Crashing Python on Import?
Question: I have a python extension that is built and installed through distutils (using
mingw on windows). However on import of this module the interpreter crashes.
Is there anyway to debug and figure out why it crashes?
I did look around online and couldn't find anything specific, or any examples.
_EDIT_
Sorry i am trying to compile for python 2.5.4 (we need 2.5.4, since we use
arcgis geoprocessor library):
<http://effbot.org/media/downloads/ftpparse-1.1-20021124.zip>
On windows, i define crash as: "Python.exe has encountered a problem and needs
to close"
I'll try debugging with GDB
_EDIT 2_ For what ever reason, doing a
setup.py clean
For the package and doing:
setup.py install
fixed all the problems. :psyduck:
Answer: I suppose using gdb see <http://oldwiki.mingw.org/index.php/gdb>
|
Python: replacing method in calendar module
Question: I'm trying to replace two methods in calendar module:
import calendar
c = calendar.HTMLCalendar(calendar.MONDAY)
def ext_formatday(self, day, weekday, *notes):
if day == 0:
return '<td class="noday"> </td>'
if len(notes) == 0:
return '<td class="%s">%d<br /></td>' % (self.cssclasses[weekday], day)
else:
return '<td class="%s">%d<br />%s</td>' % (self.cssclasses[weekday], day, notes)
def ext_formatweek(self, theweek, *notes):
if len(notes) == 0:
s = ''.join(self.formatday(d, wd) for (d, wd) in theweek)
else:
s = ''.join(self.formatday(d, wd, notes) for (d, wd) in theweek)
return '<tr>%s</tr>' % s
c.formatday = ext_formatday
c.formatweek = ext_formatweek
print c.formatmonth(2012,1,"foobar")
This won't work - could somebody point me to relevant literature or point out
what I'm doing wrong? I'm trying to implement Alan Hynes suggestion from the
following thread: [thread](http://stackoverflow.com/questions/1101524/python-
calendar-htmlcalendar/1458077#1458077) It way too late for me to think
straight and I've been dancing around that problem for over an hour.
Thanks in advance,
Jakub
Answer: Try replacing the method at the class instead of the instance.
Like this:
import calendar
def ext_formatday(self, day, weekday, *notes):
if day == 0:
return '<td class="noday"> </td>'
if len(notes) == 0:
return '<td class="%s">%d<br /></td>' % (self.cssclasses[weekday], day)
else:
return '<td class="%s">%d<br />%s</td>' % (self.cssclasses[weekday], day, notes)
def ext_formatweek(self, theweek, *notes):
if len(notes) == 0:
s = ''.join(self.formatday(d, wd) for (d, wd) in theweek)
else:
s = ''.join(self.formatday(d, wd, notes) for (d, wd) in theweek)
return '<tr>%s</tr>' % s
calendar.HTMLCalendar.formatday = ext_formatday
calendar.HTMLCalendar.formatweek = ext_formatweek
c = calendar.HTMLCalendar(calendar.MONDAY)
print c.formatmonth(2012,1,"foobar")
|
Best way to generate xml?
Question: I'm creating an web api and need a good way to very quickly generate some well
formatted xml. I cannot find any good way of doing this in python.
Note: Some libraries look promising but either lack documentation or only
output to files.
Answer: [ElementTree](http://docs.python.org/library/xml.etree.elementtree.html) is a
good module for reading xml and writing too e.g.
from xml.etree.ElementTree import Element, SubElement, tostring
root = Element('root')
child = SubElement(root, "child")
child.text = "I am a child"
print tostring(root)
Output:
<root><child>I am a child</child></root>
See this
[tutorial](http://www.doughellmann.com/PyMOTW/xml/etree/ElementTree/create.html)
for more details and how to pretty print.
Alternatively if your XML is simple, do not underestimate the power of string
formatting :)
xmlTemplate = """<root>
<person>
<name>%(name)s</name>
<address>%(address)s</address>
</person>
</root>"""
data = {'name':'anurag', 'address':'Pune, india'}
print xmlTemplate%data
Output:
<root>
<person>
<name>anurag</name>
<address>Pune, india</address>
</person>
</root>
You can use string.Template or some template engine too, for complex
formatting.
|
How to get the duration of a video in Python?
Question: I need to get the video duration in Python. The video formats that I need to
get are [MP4](http://en.wikipedia.org/wiki/MPEG-4_Part_14), Flash video,
[AVI](http://en.wikipedia.org/wiki/Audio_Video_Interleave), and MOV... I have
a shared hosting solution, so I have no
[FFmpeg](http://en.wikipedia.org/wiki/FFmpeg) support.
Answer: You'll probably need to invoke an external program.
[`ffprobe`](http://ffmpeg.org/ffprobe.html) can provide you with that
information:
import subprocess
def getLength(filename):
result = subprocess.Popen(["ffprobe", filename],
stdout = subprocess.PIPE, stderr = subprocess.STDOUT)
return [x for x in result.stdout.readlines() if "Duration" in x]
|
Python Asymmetric Encryption: Using pre-generated prv/pub keys
Question: Ok first off yes I have searched google and stackoverflow and done some
reading (over 4 hours JUST in this sitting) have not found what I need for
these reasons:
* Many of them suggest just launching an exe like gpg.exe (http://stackoverflow.com/questions/1020320)
* Some suggested using PyCrypto or other libraries and looking at them, either a) I can't find how to use any of their API, b) I can't find how to import a pre-existing prv/pub key or c) they use the insecure RandomPool (and me trying to updated it is just asking for trouble)
* Some mention it in passing but I could not find what they where linking to (or their was no link at all.
So I know ask you fellow stackoverflow users how can I do this, take a string
of a public key (or path (I could just write it to a temp file, (I plan to
just have it as a string pub_key = "..." ) ) ) and use it to sign and secure a
string (that will be posted on a forum (JSON for updating my application)?
Also these are RSA keys (Putty Gen 4096 bits SSH-2-RSA) that are generated
using PuttyGen (can be in any format (OpenSSH, ssh.com, ppk)
This is what the public key looks like
\---- BEGIN SSH2 PUBLIC KEY ----
Comment: "rsa-key-20101003"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 o+TPSK8=
\---- END SSH2 PUBLIC KEY ----
NOT THIS --> Key Format seems to be PKCS1 so M2Crypto will NOT work (its load
key function expects PEM)
Latest reading I think it is SSH Public Key File Format (RFC:
<http://www.ietf.org/rfc/rfc4716.txt> )
I also think below it wrong, I don't think it handles SSH Public Key File
Format :(
Also looks like Twisted might be where I should look
<http://www.java2s.com/Open-
Source/Python/Network/Twisted/Twisted-1.0.3/Twisted-1.0.3/twisted/conch/ssh/keys.py.htm>
Also why does SO not allow me to post a bounty immediately??
Answer: Ok I found how to load it
from twisted.conch.ssh import keys as Keys
import base64
public_key = """\
---- BEGIN SSH2 PUBLIC KEY ----
Comment: "rsa-key-20101003"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---- END SSH2 PUBLIC KEY ----"""
key_data = ''.join(public_key.splitlines()[2:-1])# remove begin, end tags and comment
blob = base64.decodestring(key_data)
key = Keys.Key._fromString_BLOB(blob)
|
Is there a python equivalent of ruby's "Pathname" module?
Question: Ruby has this really handy module called [Pathname](http://ruby-
doc.org/core/classes/Pathname.html).
Is there a python equivalent to it?
Answer: `pathlib` is the answer to all your python path woos.
Example functionality:
from pathlib import Path
p = Path.cwd()
with (p/'somefile.txt').open() as f:
f.read()
p.is_dir()
|
Python and ADNS, falling in infinite loop somewhere
Question: I have written some code that queries adns. Problem with this code is that it
gets stuck, how? Let me explain it:
* Say my dnslist is ["8.8.4.4", "8.8.8.8", "208.67.220.220", "208.67.222.222", "192.168.50.1"]
* It would pop a dns from the list and query againt it, now that means that DNS will be queried in reverse order
* No matter what i do, It never shows results from the dns it picked up first (in our case 192.168.50.1)
* I was not sure if that dns ever replied so
* First i changed DNS list to contain just that last DNS Server and code executes fine
* Second i used the old list with 5 DNS servers except that the last one was managed by my so i could track if code even queries it or not, and to my surprise the query does take place.
* So query is made, we get result but that result is never inserted into resolved_hosts for some reason, and because that results is not inserted, its length will remain less than the length of dnslist, causing a infinite loop.
What do you think could be causing this problem and how to solve it?
# Code Execution Results
Inside class's init'
Data
host www.yahoo.com
dnslist length 5
intensity 1
Inside resolve()
inside finished_resolving()
Resolved : 0/5
Inside 'while not finished_resolving'
Queue: 0/1
Launching Querying for www.yahoo.com/1 on 192.168.50.1
Queue: 1/1
Launching Querying for www.yahoo.com/1 on 208.67.222.222
inside collect_results()
inside finished_resolving()
Resolved : 0/5
Inside 'while not finished_resolving'
------------------------ CLIPPED ----------------
Inside 'while not finished_resolving'
inside collect_results()
Inside collect_results's for query in self.adns.completed()
DNS used was208.67.222.222
Answered : (0, 'any-fp.wa1.b.yahoo.com', 1286169807, ('69.147.125.65', '67.195.160.76'))
Resolved www.yahoo.com to 69.147.125.65 using 208.67.222.222
Resolved hosts count1
And they are:
{'208.67.222.222': '69.147.125.65'}
inside finished_resolving()
Resolved : 1/5
Inside 'while not finished_resolving'
Queue: 1/1
Launching Querying for www.yahoo.com/1 on 208.67.220.220
inside collect_results()
inside finished_resolving()
Resolved : 1/5
Inside 'while not finished_resolving'
-------------------------- CLIPPED --------------------
inside collect_results()
Inside collect_results's for query in self.adns.completed()
DNS used was208.67.220.220
Answered : (0, 'any-fp.wa1.b.yahoo.com', 1286169790, ('67.195.160.76', '69.147.125.65'))
Resolved www.yahoo.com to 67.195.160.76 using 208.67.220.220
Resolved hosts count2
And they are:
{'208.67.222.222': '69.147.125.65', '208.67.220.220': '67.195.160.76'}
inside finished_resolving()
Resolved : 2/5
Inside 'while not finished_resolving'
Queue: 1/1
Launching Querying for www.yahoo.com/1 on 8.8.8.8
inside collect_results()
inside finished_resolving()
Resolved : 2/5
Inside 'while not finished_resolving'
-------------------------- CLIPPED --------------------
inside collect_results()
Inside collect_results's for query in self.adns.completed()
DNS used was8.8.8.8
Answered : (0, 'eu-fp.wa1.b.yahoo.com', 1286169758, ('87.248.122.122',))
Resolved www.yahoo.com to 87.248.122.122 using 8.8.8.8
Resolved hosts count3
And they are:
{'208.67.222.222': '69.147.125.65', '208.67.220.220': '67.195.160.76', '8.8.8.8': '87.248.122.122'}
inside finished_resolving()
Resolved : 3/5
Inside 'while not finished_resolving'
Queue: 1/1
Launching Querying for www.yahoo.com/1 on 8.8.4.4
inside collect_results()
inside finished_resolving()
Resolved : 3/5
Inside 'while not finished_resolving'
-------------------- CLIPPED -------------------------------------
inside collect_results()
Inside collect_results's for query in self.adns.completed()
DNS used was8.8.4.4
Answered : (0, 'eu-fp.wa1.b.yahoo.com', 1286169757, ('87.248.122.122',))
Resolved www.yahoo.com to 87.248.122.122 using 8.8.4.4
Resolved hosts count4
And they are:
{'208.67.222.222': '69.147.125.65', '208.67.220.220': '67.195.160.76', '8.8.8.8': '87.248.122.122', '8.8.4.4': '87.248.122.122'}
inside finished_resolving()
Resolved : 4/5
Inside 'while not finished_resolving'
inside collect_results()
inside finished_resolving()
Resolved : 4/5
---------------- CLIPPED -------------------------------
(last block keeps repeating until system starts to hang up, load goes upto 24)
# Code
**test.py**
import adns
from time import time
from async_dns import AsyncResolver
dnslist2 = ["8.8.4.4", "8.8.8.8", "208.67.220.220", "208.67.222.222", "192.168.50.1"] #192.168.50.1 is a dns server i manage
host = "www.yahoo.com"
record = adns.rr.A
intensity = len(dnslist2)/5+1
ar = AsyncResolver(dnslist2, host, record, intensity)
start = time()
resolved = ar.resolve()
end = time()
print "\n\n"
for dns, ip in resolved.items():
if ip is None:
print "%s could not resolv %s." % (dns, host)
else:
print "%s resolved it to %s : %s" % (dns, host, ip)
print "\n\n----------------------------------------------------"
print "It took %.2f seconds to query %d dns." % (end-start, len(dnslist))
print "----------------------------------------------------"
**async_dns.py**
#!/usr/bin/python
#
import sys
import adns
from time import time
class AsyncResolver(object):
def __init__(self, dnslist, host, record, intensity=10):
"""
dnslist: a list of dns used to resolve
host : hostname to resolve
record: recordtype to resolve
intensity: how many hosts to resolve at once
"""
print "Inside class's init'"
self.dnslist = dnslist
self.host = host
self.record = record
if intensity >= len(dnslist) :
self.intensity = len(dnslist)/5+1
else:
self.intensity = intensity
print "Data"
print "host " + host
print "dnslist length " + str(len(dnslist))
print "intensity " + str(intensity)
def resolve(self):
""" Resolves hosts and returns a dictionary of { 'dns': 'ip' }. """
print "Inside resolve()"
host = self.host
record = self.record
resolved_hosts = {}
active_queries = {}
dns_queue = self.dnslist[:]
def collect_results():
print "inside collect_results()"
for query in self.adns.completed():
print "Inside collect_results's for query in self.adns.completed()"
answer = query.check()
dns = active_queries[query]
print "DNS used was" + dns
print "Answered : " + str(answer)
del active_queries[query]
if answer[0] == 0:
#print "Inside answer[0] == 0 , ip:" + answer[3][0]
ip = answer[3][0]
resolved_hosts[dns] = ip
print "Resolved %s to %s using %s" % (host, ip, dns)
print "Resolved hosts count" + str(len(resolved_hosts))
print "And they are: "
print str(resolved_hosts)
print "\n"
elif answer[0] == 101 and not record == adns.rr.CNAME: # CNAME if CNAME wasn't required'
print "ooopppps, i got a CNAME, gotta find its A"
print "\n"
query = self.adns.submit(answer[1], adns.rr.A)
active_queries[query] = dns
else:
resolved_hosts[dns] = None
print "THIS COULD NOT BE RESOLVED"
def finished_resolving():
print "inside finished_resolving()"
print "Resolved : " + str(len(resolved_hosts)) + "/" + str(len(self.dnslist))
return len(resolved_hosts) == len(self.dnslist)
while not finished_resolving():
print "Inside 'while not finished_resolving'"
while dns_queue and len(active_queries) <= self.intensity:
print "Queue: " + str(len(active_queries)) + "/" + str(self.intensity)
dns = dns_queue.pop()
self.adns = adns.init(adns.iflags.noautosys,sys.stderr,"nameserver "+dns)
query = self.adns.submit(host, record)
print "Launching Querying for " + host + "/" + str(record) + " on " + dns
active_queries[query] = dns
collect_results()
return resolved_hosts
Answer: I have just attempted to use adns python binding and have experienced a
similar problem - the completed queries array never gets completely filled,
causing the check loop to run forever. In my case, it appeared that domains
that could not be resolved (due to NXDOMAIN etc) were never added to the
completed queries array (with empty/Null value)
I had a look at the C binding but could not see a separate data structure for
holding failed results, so it does appear that these should be added to the
'completed' queries somehow. I suspect there is a bug in the binding or adns
library preventing this from happening.
|
Python doctest example failure
Question: This is probably a silly question.
I am experimenting with python doctest, and I try to run
[this](http://docs.python.org/library/doctest.html#simple-usage-checking-
examples-in-a-text-file) example
ending with
if __name__ == "__main__":
import doctest
doctest.testfile("example.txt")
I have put "example.txt" in the same folder as the source file containing the
example code, but I get the following error:
Traceback (most recent call last):
File "test_av_funktioner.py", line 61, in <module>
doctest.testfile("example.txt")
File "C:\Python26\lib\doctest.py", line 1947, in testfile
text, filename = _load_testfile(filename, package, module_relative)
File "C:\Python26\lib\doctest.py", line 219, in _load_testfile
return open(filename).read(), filename
IOError: [Errno 2] No such file or directory: 'example.txt'
Can I somehow tell/set where the doctest module is searching for the specified
file?
Answer: Doctest searches relative to the calling module's directory by default (but
you can override this).
Quoting the docs for
[`doctest.testfile`](http://docs.python.org/library/doctest.html#doctest.testfile):
> Optional argument `module_relative` specifies how the filename should be
> interpreted:
>
> * If `module_relative` is **True** (the default), then `filename`
> specifies an OS-independent module-relative path. By default, this path is
> relative to the calling module’s directory; but if the `package` argument is
> specified, then it is relative to that package. To ensure OS-independence,
> `filename` should use `/` characters to separate path segments, and may not
> be an absolute path (i.e., it may not begin with `/`).
> * If `module_relative` is **False** , then `filename` specifies an OS-
> specific path. The path may be absolute or relative; relative paths are
> resolved with respect to the current working directory.
>
|
How to distinguish between a sequence and a mapping
Question: I would like to perform an operation on an argument based on the fact that it
might be a map-like object or a sequence-like object. I understand that no
strategy is going to be 100% reliable for type-like checking, but I'm looking
for a robust solution.
Based on this [answer](http://stackoverflow.com/questions/305359/correct-way-
to-detect-sequence-parameter/425567#425567), I know how to determine whether
something is a sequence and I can do this check after checking if the object
is a map.
def ismap(arg):
# How to implement this?
def isseq(arg):
return hasattr(arg,"__iter__")
def operation(arg):
if ismap(arg):
# Do something with a dict-like object
elif isseq(arg):
# Do something with a sequence-like object
else:
# Do something else
Because a sequence can be seen as a map where keys are integers, should I just
try to find a key that is not an integer? Or maybe I could look at the string
representation? or...?
**UPDATE**
I selected SilentGhost's answer because it looks like the most "correct" one,
but for my needs, here is the solution I ended up implementing:
if hasattr(arg, 'keys') and hasattr(arg, '__getitem__'):
# Do something with a map
elif hasattr(arg, '__iter__'):
# Do something with a sequence/iterable
else:
# Do something else
Essentially, I don't want to rely on an ABC because there are many custom
classes that behave like sequences and dictionary but that still do not extend
the python collections ABCs (see @Manoj comment). I thought the keys attribute
(mentioned by someone who removed his/her answer) was a good enough check for
mappings.
Classes extending the Sequence and Mapping ABCs will work with this solution
as well.
Answer:
>>> from collections import Mapping, Sequence
>>> isinstance('ac', Sequence)
True
>>> isinstance('ac', Mapping)
False
>>> isinstance({3:42}, Mapping)
True
>>> isinstance({3:42}, Sequence)
False
[`collections` abstract base classes
(ABCs)](http://docs.python.org/library/collections.html#abcs-abstract-base-
classes)
|
How to write tag deleter script in python
Question: I want to implement a file reader (folders and subfolders) script which
detects some tags and delete those tags from the files.
The files are .cpp, .h .txt and .xml And they are hundreds of files under same
folder.
I have no idea about python, but people told me that I can do it easily.
**EXAMPLE** :
My main folder is A: C:\A
Inside A, I have folders (B,C,D) and some files A.cpp A.h A.txt and A.xml. In
B i have folders B1, B2,B3 and some of them have more subfolders, and files
.cpp, .xml and .h....
* xml files, contains some tags like `<!-- $Mytag: some text$ -->`
* .h and .cpp files contains another kind of tags like `//$TAG some text$`
* .txt has different format tags: `#$This is my tag$`
It always starts and ends with $ symbol but it always have a comment character
(//,
The idea is to run one script and delete all tags from all files so the script
must:
* Read folders and subfolders
* Open files and find tags
* If they are there, delete and save files with changes
**WHAT I HAVE:**
import os
for root, dirs, files in os.walk(os.curdir):
if files.endswith('.cpp'):
%Find //$ and delete until next $
if files.endswith('.h'):
%Find //$ and delete until next $
if files.endswith('.txt'):
%Find #$ and delete until next $
if files.endswith('.xml'):
%Find <!-- $ and delete until next $ and -->
Answer: The general solution would be to:
1. use the `os.walk()` function to traverse the directory tree.
2. Iterate over the filenames and use `fn_name.endswith('.cpp')` with if/elseif to determine which file you're working with
3. Use the `re` module to create a regular expression you can use to determine if a line contains your tag
4. Open the target file and a temporary file (use the `tempfile` module). Iterate over the source file line by line and output the filtered lines to your tempfile.
5. If any lines were replaced, use `os.unlink()` plus `os.rename()` to replace your original file
It's a trivial excercise for a Python adept but for someone new to the
language, it'll probably take a few hours to get working. You probably
couldn't ask for a better task to get introduced to the language though. Good
Luck!
\----- Update -----
The `files` attribute returned by os.walk is a list so you'll need to iterate
over it as well. Also, the `files` attribute will only contain the base name
of the file. You'll need to use the `root` value in conjunction with
`os.path.join()` to convert this to a full path name. Try doing just this:
for root, d, files in os.walk('.'):
for base_filename in files:
full_name = os.path.join(root, base_filename)
if full_name.endswith('.h'):
print full_name, 'is a header!'
elif full_name.endswith('.cpp'):
print full_name, 'is a C++ source file!'
If you're using Python 3, the print statements will need to be function calls
but the general idea remains the same.
|
m2crypto: python 2.7 compatibility and which version of OpenSSL to use?
Question: We've been using M2crypto with Python 2.6 for Windows (32-bit) for some time
with great success. We used one of the user contributed setups to install
M2crypto in our development environments. We would like to move to Python 2.7,
but noticed there are no pre-built Python 2.7 setups for m2crypto.
Questions:
1. Is M2crypto 0.20.2 compatible with Python 2.7 or should we remain at Python 2.6 if we want to continue to use this library?
2. Does anyone have a user built setup for installing M2Crypto 0.20.2 in a Python 2.7 environment? (There are no 2.7 contributions on the M2crypto site and google comes up empty as well)
3. Can we copy our Python 2.6 M2Crypto files (under lib\site-packages\M2Crypto) to the same place in our Python 2.7 setup and avoid a formal installation process?
4. What version of OpenSLL should we use with M2crypto 0.20.2? I checked the OpenSSL website and there appear 2 versions of OpenSSL to choose from: 0.9.8 and 1.0.0a.
Thank you, Malcolm
Answer: 1. Yes, it's compatible with Python 2.7, so you can freely upgrade if you have not already.
2. Yes, here you have `[bdist_wininst](http://myfreefilehosting.com/f/23acda828e_0.33MB)`, `[bdist_egg](http://myfreefilehosting.com/f/e5e68275ff_0.23MB)` and `[bdist](http://myfreefilehosting.com/f/6235a73fed_0.24MB)` for M2Crypto 20.2 built for Python 2.7 with MSVS2008 by me, hope it will fit your needs.
3. No, you will get import error, as .pyd file (which is actually DLL) has `python26.dll` in it's import table, so this will not work. Of course, you can hack it and replace `python26` with `python27`, but that's too dirt and gives you no guarantee it will work all the time.
4. Version I uploaded for you works fine with OpenSSL 0.9.8o, haven't tested it with 1.0.0.
|
programmatically find and replace content dynamically in a string in python
Question: i need to find and replace patterns in a string with a dynamically generated
content.
lets say i want to find all strings within '' in the string and double the
string. a string like:
`my 'cat' is 'white'` should become my `'catcat' is 'whitewhite'`
all matches could also appear twice in the string.
thank you
Answer: Make use of the power of [regular
expressions](http://docs.python.org/library/re.html). In this particular case:
import re
s = "my 'cat' is 'white'"
print re.sub("'([^']+)'", r"'\1\1'", s) # prints my 'catcat' is 'whitewhite'
`\1` refers to the first group in the regex (called `$1` in some other
implementations).
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Importing assemblies into IronPython from another assembly
Question: I have an IronPython 2.6/2.7 script I am writing which imports a lot of
assemblies.
In other words, at the top of the script it does this...
clr.AddReference( "System.Xml" )
import System.Xml
Except it doesn't do this for 1 assembly, but for 10 assemblies.
Some of the modules are built-in .NET assembllies and some are assemblies I
have made.
I'd like to simplify my script so that it loads one assembly that I will
build. I want to then call a method in that assembly that will do the
"AddReference" and "import" for the 10 assemblies. The primary goal of all
this is to minimize the length/complexity of the script.
So in the end I would see it working like this
clr.AddReferenceToFileAndPath( "d:\\myassembly" )
import MyAssembly
MyAssembly.ImportAllAssembliesIReallyWant()
My core problemis despite reading all the information I could find on
ScriptRuntime, ScriptEngine, scopes, etc. - I still can't figure out how to
write a method in "MyAssembly" that affects what modules are loaded in the
calling script.
Answer: One way to go about this would be to create a built-in module which does this.
You can do this with:
[assembly: PythonModule("mymodule", typeof(MyModuleType)]
public static class MyModuleType {
[SpecialName]
public static void PerformModuleReload(PythonContext context, PythonDictionary dict) {
context.DomainManager.LoadAssembly(typeof(TypeInAssemblyToLoad));
}
}
Just add appropriate LoadAssembly calls for all of the assemblies you care
about. The assembly could also populate members in dict that you want
available.
Another (and possibly simpler) way would be to simply have a .py file which
does all of the clr.AddReference calls you need and have every module import
that one file. The import mechanism will do the appropriate caching so it will
only load once but will ensure all of the assemblies are available for each
module which needs them.
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How to bulk insert data to mysql with python
Question: Currently i'm using Alchemy as a ORM, and I look for a way to speed up my
insert operation, I have bundle of XML files to import
for name in names:
p=Product()
p.name="xxx"
session.commit()
i use above code to insert my data paser from batch xml file to mysql,it's
very slow also i tried to
for name in names:
p=Product()
p.name="xxx"
session.commit()
but it seems didn't change anything
Answer: You could bypass the ORM for the insertion operation and use the [SQL
Expression
generator](http://www.sqlalchemy.org/docs/core/tutorial.html?highlight=insert#insert-
expressions) instead.
Something like:
conn.execute(Product.insert(), [dict(name=name) for name in names])
That should create a single statement to do your inserting.
That example was taken from [lower down the same
page](http://www.sqlalchemy.org/docs/core/tutorial.html?highlight=insert#executing-
multiple-statements).
(I'd be interested to know what speedup you got from that)
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Subsets and Splits