# question: how do you sort on the second element in a list of tuples
>>> l = [ 'z', 'h', 'a' ]
>>> sorted(l)
Out[35]: ['a', 'h', 'z']
>>> lstr = [ ('z', 2), ('h', 1), ('a', 3), ('a', 4) ]
>>> sorted(lstr)
Out[37]: [('a', 3), ('a', 4), ('h', 1), ('z', 2)]
>>> sorted(lstr, reverse=True)
Out[38]: [('z', 2), ('h', 1), ('a', 4), ('a', 3)]

# option 1: change the order of the tuple into the order you want it sorted
>>> lnum = [ (2, 'z'), (1, 'h'), (4, 'a'), (3, 'a') ]
>>> sorted(lnum, reverse=True)
Out[41]: [(4, 'a'), (3, 'a'), (2, 'z'), (1, 'h')]
# and then change it back to the order you want to use it
>>> numl = [ (i2, i1) for (i1, i2) in lnum ]
>>> numl
Out[43]: [('z', 2), ('h', 1), ('a', 4), ('a', 4)]

# option 2: use python function to retrieve the appropriate item when sorting
>>> import operator
>>> sorted(lstr, key=operator.itemgetter(1))
Out[45]: [('h', 1), ('z', 2), ('a', 3), ('a', 4)]
>>> sorted(lstr, key=operator.itemgetter(1), reverse=True)
Out[47]: [('a', 4), ('a', 3), ('z', 2), ('h', 1)]