## Can build up a dict by starting with the the empty dict {}
## and storing key/value pairs into the dict like this:
## dict[key] = value-for-that-key
dict = {}
dict['a'] = 'alpha'
dict['g'] = 'gamma'
dict['o'] = 'omega'

print dict

print dict['a']
dict['a'] = 6
print dict['a']
'a' in dict

print dict['z']                  ## Throws KeyError

if 'z' in dict: print dict['z']     ## Avoid KeyError

print dict.get('z')  ## None (instead of KeyError)

"""
Explanation: Dict Hash Table
Python's efficient key/value hash table structure is called a "dict". The contents of a dict can be written as a series of key:value pairs within braces { }, e.g. dict = {key1:value1, key2:value2, ... }. The "empty dict" is just an empty pair of curly braces {}.
Looking up or setting a value in a dict uses square brackets, e.g. dict['foo'] looks up the value under the key 'foo'. Strings, numbers, and tuples work as keys, and any type can be a value. Other types may or may not work correctly as keys (strings and tuples work cleanly since they are immutable). Looking up a value which is not in the dict throws a KeyError -- use "in" to check if the key is in the dict, or use dict.get(key) which returns the value or None if the key is not present (or get(key, not-found) allows you to specify what value to return in the not-found case).
End of explanation
"""


## By default, iterating over a dict iterates over its keys.
## Note that the keys are in a random order.
for key in dict: print key


## Exactly the same as above
for key in dict.keys(): print key

## Get the .keys() list:
print dict.keys()

## Likewise, there's a .values() list of values
print dict.values()  ## ['alpha', 'omega', 'gamma']

## Common case -- loop over the keys in sorted order,
## accessing each key/value
for key in sorted(dict.keys()):
    print key, dict[key]

## .items() is the dict expressed as (key, value) tuples
print dict.items()

## This loop syntax accesses the whole dict by looping
## over the .items() tuple list, accessing one (key, value)
## pair on each iteration.
for k, v in dict.items(): print k, '>', v

"""
Explanation: A for loop on a dictionary iterates over its keys by default. The keys will appear in an arbitrary order. The methods dict.keys() and dict.values() return lists of the keys or values explicitly. There's also an items() which returns a list of (key, value) tuples, which is the most efficient way to examine all the key value data in the dictionary. All of these lists can be passed to the sorted() function.
End of explanation
"""


hash = {}
hash['word'] = 'garfield'
hash['count'] = 42
s = 'I want %(count)d copies of %(word)s' % hash
s

"""
Explanation: There are "iter" variants of these methods called iterkeys(), itervalues() and iteritems() which avoid the cost of constructing the whole list -- a performance win if the data is huge. However, I generally prefer the plain keys() and values() methods with their sensible names.
Strategy note: from a performance point of view, the dictionary is one of your greatest tools, and you should use where you can as an easy way to organize data. For example, you might read a log file where each line begins with an ip address, and store the data into a dict using the ip address as the key, and the list of lines where it appears as the value. Once you've read in the whole file, you can look up any ip address and instantly see its list of lines. The dictionary takes in scattered data and make it into something coherent.
Dict Formatting
The % operator works conveniently to substitute values from a dict into a string by name:
End of explanation
"""


var = 6
del var  # var no more!
var

list = ['a', 'b', 'c', 'd']
del list[0]     ## Delete first element
del list[-2:]   ## Delete last two elements
print list

dict = {'a':1, 'b':2, 'c':3}
del dict['b']   ## Delete 'b' entry
print dict

"""
Explanation: Del
The "del" operator does deletions. In the simplest case, it can remove the definition of a variable, as if that variable had not been defined. Del can also be used on list elements or slices to delete that part of the list and to delete entries from a dictionary.
End of explanation
"""


  # Echo the contents of a file
  f = open('data/poem.txt', 'rU')
  for line in f:   ## iterates over the lines of the file
    print line,    ## trailing , so print does not add an end-of-line char
                   ## since 'line' already includes the end-of line.
  f.close()

"""
Explanation: Files
The open() function opens and returns a file handle that can be used to read or write a file in the usual way. The code f = open('name', 'r') opens the file into the variable f, ready for reading operations, and use f.close() when finished. Instead of 'r', use 'w' for writing, and 'a' for append. The special mode 'rU' is the "Universal" option for text files where it's smart about converting different line-endings so they always come through as a simple '\n'. The standard for-loop works for text files, iterating through the lines of the file (this works only for text files, not binary files). The for-loop technique is a simple and efficient way to look at all the lines in a text file:
End of explanation
"""


