Python trying to write and read class from file but something went horribly wrong
Question: Considering this is only for my homework I don't expect much help but I just
can't figure this out and honestly I can't get my head around what's going
wrong. Usually I have an idea where the problem is but now I just don't get
it.

_Long story short_ : I'm trying to create a valid looking telephone number
within a class and then loading it onto an array or list then later on save
all of them as string into a folder. When I start the program again I want it
to read the file and re-create my class and load it back into the list.
(Basically a very simple repository).

Problem is even though I evaluate the stored phone number in the exact same
way I validate it as input data ... I get an error which makes no sens.

Another small problem is the fact that when I re-use the data for some reason
it creates white spaces in the file which in turn messes my program up badly.

Here I validate phone numbers:

    
    
    def validateTel(call_ID):
        if isinstance (call_ID, str) == True:
            call_ID = call_ID.replace (" ", "")
            if (len (call_ID) != 10):
                print ("Telephone numbers are 10 digits long")
                return False
            for item in call_ID:
                try:
                    int(item)
                except:
                    print ("Telephone numbers should contain non-negative digits")
                    return False
                else:
                    if (int(item) < 0):
                    print ("Digits are non-negative")
    

After this I use it and other non-relevant (to this discussion) data to create
an object (class instance) and move them to a list.

Inside my class I have a load from string and a load to string. What they do
is take everything from my class object so I can write it to a file using
`"+"` as a separator so I can use `string.split("+")` and write it to a file.
This works nicely, but when I read it ... well it's not working.

    
    
        def load_data():
            f = open ("data.txt", "r")
            ch = f.read()
            contact = agenda.contact () # class object
            if ch in (""," ","None"," None"):
               f.close()
               return []  # if the file is empty or has None in some way I pass an empty stack
            else:
               stack = [] # the list where I load all my class objects
            f.seek(0,0)
            for line in f:
                contact.loadFromString(line) # explained bellow
                stack.append(deepcopy(contact))
            f.close()
            return stack
    

In `loadFromString(line)` all I do is validate the line (see if the data
inside it at least looks OK).

Now here is the place where I validate the string I just read from the file:

    
    
    def validateString (load_string):
        string = string.split("+")
        if len (string) != 4:
            print ("System error in loading from file: Program skipping segment of corrupt data")
            return False
        if string[0] == "" or string[0] == " " or string[0] == None or string[0] == "None" or string[0] == " None":
            print ("System error in loading from file: Name field cannot be empty")
        try:
            int(string[1])
        except:
            print("System error in loading from file: ID is not integer")
            return False
        if (validateTel(str(string[2])) == False):
            print ("System error in loading from file: Call ID (telephone number)")
            return False
        return True
    

**Small recap** : I try to load the data from file using `loadFromString()`.
The only relevant thing that does is it tries to validate my data with
`validateString(string)` in there the only thing that messes me up is the
validateTel. But my input data gets validated in the same way my stored data
does. They are perfectly identical but it gives a "System error" BUT to give
such an error it should have also gave an error in the validate sub-program
but it doesn't.

I hope this is enough info because my program is kinda big (for me any way)
however the bug should be here somewhere.

I thank anyone brave enough to sift trough this mess.

EDIT:

The class is very simple, it looks like this:

    
    
        class contact:
             def __init__ (self, name = None, ID = None, tel = None, address = None):
                 self.__name = name
                 self.__id = ID
                 self.__tel = tel
                 self.__address = address
    

After this I have a series of setters and getters (to modify contacts and to
return parts of the abstract data)

Here I also have my loadFromString and loadToString but those work just fine
(except maybe they cause a small jump after each line (an empty line) which
then kills my program, but that I can deal with)

My problem is somewhere in the validate or a way the repository interacts with
it. The point is that even if it gives an error in the loading of the data,
first the validate should print an error ... but it doesn't -_-


Answer: You said `I just can't figure this out and honestly I can't get my head around
what's going wrong`. I think this is a great quote which sums up a large part
of programming and software development in general -- dealing with crazy,
weird problems and spending a lot of time trying to wrap your head around
them.

Figuring out how to turn ridiculously complicated problems into small,
manageable problems is the hardest part of programming, but also arguably the
most important and valuable.

* * *

Here's some general advice which I think might help you:

  * use meaningful names for functions and variables (`validateString` doesn't tell me anything about what the function does; `string` tells me nothing about the meaning of its contents)
  * break down problems into small, well-defined pieces
  * specify your data -- **what is a phone number?** 10 positive digits, no spaces, no punctuation?
  * document/comment the input/output from functions if it's not obvious

Specific suggestions:

  * `validateTel` could probably be replaced with a simple regular expression match
  * try using `json` for serialization
  * if you're using `json`, then it's easy to use lists. I would strongly recommend this over using `+` as a separator -- that looks highly questionable to me

* * *

Example: using a regex

    
    
    import re
    
    def validateTel(call_ID):
        phoneNumberRegex = re.compile("^\d{10}$") # match a string of 10 digits
        return phoneNumberRegex.match(call_ID)
    

Example: using json

    
    
    import json
    phoneNumber1, phoneNumber2, phoneNumber3 = ... whatever ...
    mylist = [phoneNumber1, phoneNumber2, phoneNumber3]
    print json.dumps(mylist)
    

