Core Python Programming (2nd Edition)

Python dictionaries are implemented as resizeable hash tables. If you are familiar with Perl, then we can
say that dictionaries are similar to Perl's associative arrays or hashes.
We will now take a closer look at Python dictionaries. The syntax of a dictionary entry is key:value Also,
dictionary entries are enclosed in braces ( { } ).
How to Create and Assign Dictionaries
Creating dictionaries simply involves assigning a dictionary to a variable, regardless of whether the
dictionary has elements or not:
>>> dict1 = {}
>>> dict2 = {'name': 'earth', 'port': 80}
>>> dict1, dict2
({}, {'port': 80, 'name': 'earth'})
In Python versions 2.2 and newer, dictionaries may also be created using the factory function dict().
We discuss more examples later when we take a closer look at dict(), but here's a sneak peek for now:
>>> fdict = dict((['x', 1], ['y', 2]))
>>> fdict
{'y': 2, 'x': 1}
In Python versions 2.3 and newer, dictionaries may also be created using a very convenient built-in
method for creating a "default" dictionary whose elements all have the same value (defaulting to None if
not given), fromkeys():
>>> ddict = {}.fromkeys(('x', 'y'), -1)
>>> ddict
{'y': -1, 'x': -1}
>>>
>>> edict = {}.fromkeys(('foo', 'bar'))
>>> edict
{'foo': None, 'bar': None}
How to Access Values in Dictionaries
To traverse a dictionary (normally by key), you only need to cycle through its keys, like this: