Mapping types – dictionaries
Of all the built-in Python data types, the dictionary is probably the most interesting one. It's the only standard mapping type, and it is the backbone of every Python object.
A dictionary maps keys to values. Keys need to be hashable objects, while values can be of any arbitrary type. Dictionaries are mutable objects.
There are quite a few different ways to create a dictionary, so let me give you a simple example of how to create a dictionary equal to {'A': 1, 'Z': -1} in five different ways:
>>> a = dict(A=1, Z=-1) >>> b = {'A': 1, 'Z': -1} >>> c = dict(zip(['A', 'Z'], [1, -1])) >>> d = dict([('A', 1), ('Z', -1)]) >>> e = dict({'Z': -1, 'A': 1}) >>> a == b == c == d == e # are they all the same? True # indeed!
Have you noticed those double equals? Assignment is done with one equal, while to check whether an object is the same as another one (or 5 in one go, in this case), we use double equals. There is also...