how can I sort a bunch of lists over multiple fields?

[Lonnie Princehouse]

key and cmp are equivalent for non-trivial cases (defined below), and
for trivial cases the performance will be a trade-off between more
function calls with cmp versus more memory use with key.  Granted, for
the smallish lists that the majority of Python sorts are done on, key
is probably the better choice.

Non-trivial:
  Any time the user decides to (1) cache intermediary results for a cmp
function or (2) define a __cmp__ function for the key return value.
These arise when comparison of partial keys is often sufficient to
establish order between two objects.