Python 2.5.2 (r252:60911, Feb 22 2008, 07:57:53) 
[GCC 4.0.1 (Apple Computer, Inc. build 5363)]
Type "help", "copyright", "credits" or "license" for more information.
>>> #dictionaries
>>> emissions = {1799:1, 1800:70, 1801: 74, 1902: 215630}
>>> emissions
{1800: 70, 1801: 74, 1902: 215630, 1799: 1}
>>> emissions[1800] # get value associated with key 1800
70
>>> emissions[1801] = 75.4 # update value associated with key 1801
>>> emissions
{1800: 70, 1801: 75.400000000000006, 1902: 215630, 1799: 1}
>>> # the length is the number of key, item pairs
>>> len(emissions)
4
>>> # we can use a for loop to iterate over elements
>>> for k in emissions:
... 	print k,emissions[k]
... 
1800 70
1801 75.4
1902 215630
1799 1
>>> # above shows that you are iterating over the keys
>>> #methods for dictionaries
>>> emissions.keys()
[1800, 1801, 1902, 1799]
>>> emissions.values()
[70, 75.400000000000006, 215630, 1]
>>> emissions.items() # the key, value pairs as tuples
[(1800, 70), (1801, 75.400000000000006), (1902, 215630), (1799, 1)]
>>> emissions.get(1801)
75.400000000000006
>>> emissions.get(2009) # no error!
>>> emissions.get(2009,-3) #  you can specify value to return if no key
-3
>>> #compare to this
>>> print emissions[2009]
Traceback (most recent call last):
  File "<string>", line 1, in <string>
KeyError: 2009
>>> # get doesn't give you this error
>>> # add dict2 contents to dict1:
>>> dict1 = {'444-3333':'Dale','111-2222':'Sally'}
>>> dict2 = {'456-2345':'Tom','333-4444':'Bill'}
>>> dict1.update(dict2)
>>> dict1
{'111-2222': 'Sally', '333-4444': 'Bill', '444-3333': 'Dale', '456-2345': 'Tom'}
>>> # of course, this leaves dict2 alone
>>> dict2
{'333-4444': 'Bill', '456-2345': 'Tom'}
>>> # we did some code in the shell here, but
>>> # that code is in a neater form in inverted_dict.py
>>>