# lists associate a number with each item in the list
>>> l = [ 'a', 'b', 'c' ]
>>> l[0]
Out[3]: 'a'

# dictionaries associate any immutable type with each item
>>> d = { }
>>> type(d)
Out[5]: dict
>>> d['a'] = 1
>>> d['b'] = 13
>>> d
Out[8]: {'a': 1, 'b': 13}
>>> d[(1, 2, 3)] = 'abc'
>>> d
Out[10]: {'a': 1, 'b': 13, (1, 2, 3): 'abc'}
# lists are mutable, so cannot be used as a key
>>> d[[1, 2, 3]] = 'def'
Traceback (most recent call last):
  File "/Users/rcd/Library/Enthought/Canopy_64bit/User/lib/python2.7/site-packages/IPython/core/interactiveshell.py", line 2721, in run_code
    exec code_obj in self.user_global_ns, self.user_ns
  File "<ipython-input-11-81db1c0040e5>", line 1, in <module>
    d[[1, 2, 3]] = 'def'
TypeError: unhashable type: 'list'

# the values associated with each key can be changed though
>>> d['a'] += 1
>>> d
Out[13]: {'a': 2, 'b': 13, (1, 2, 3): 'abc'}
>>> d['def'] = [1, 2, 3]
>>> d['def'] += [1]
>>> d
Out[16]: {'a': 2, 'b': 13, 'def': [1, 2, 3, 1], (1, 2, 3): 'abc'}

# it is an error to try to access a key that does not exist in the dictionary
>>> d['z'] += 1
Traceback (most recent call last):
  File "/Users/rcd/Library/Enthought/Canopy_64bit/User/lib/python2.7/site-packages/IPython/core/interactiveshell.py", line 2721, in run_code
    exec code_obj in self.user_global_ns, self.user_ns
  File "<ipython-input-17-b3482c982944>", line 1, in <module>
    d['z'] += 1
KeyError: 'z'
>>> d['z'] = 1
>>> d['z'] += 1
>>> d
Out[20]: {'a': 2, 'b': 13, 'def': [1, 2, 3, 1], 'z': 2, (1, 2, 3): 'abc'}

# there are a variety of ways to access the information in a dictionary
>>> d.keys()
Out[21]: ['a', 'b', 'z', 'def', (1, 2, 3)]
>>> d.values()
Out[22]: [2, 13, 2, [1, 2, 3, 1], 'abc']
>>> m = max(d.keys())
>>> m
Out[25]: (1, 2, 3)
# note, the lists returned by keys and values are parallel structures
>>> d.keys().index(m)
Out[26]: 4
>>> d.values()[4]
Out[28]: 'abc'
# items is the shorthand for getting both keys and values together
>>> d.items()
Out[29]: [('a', 2), ('b', 13), ('z', 2), ('def', [1, 2, 3, 1]), ((1, 2, 3), 'abc')]
# another way to do the same thing
>>> zip(d.keys(), d.values())
Out[30]: [('a', 2), ('b', 13), ('z', 2), ('def', [1, 2, 3, 1]), ((1, 2, 3), 'abc')]

# looping over the items in a dictionary: two ways
>>> for item in d.items():
...     print(str(item[0]) + '\t' + str(item[1]))
...   
a	2
b	13
z	2
def	[1, 2, 3, 1]
(1, 2, 3)	abc
>>> for (k,v) in d.items():
...     print(str(k) + '\t' + str(v))
...     
a	2
b	13
z	2
def	[1, 2, 3, 1]
(1, 2, 3)	abc