From Python docs: http://docs.python.org/library/stdtypes.html#comparisons
Implementation note: Objects of different types except numbers are ordered by their type names; objects of the same types that don’t support proper comparison are ordered by their address.
Is there any reason for choosing to do this over raising an exception?
It can be useful for objects of different types to be collected into a single, sorted list, in a definite order. By giving all objects a stable sort order, this behavior is default.
About four lines up from that line you quoted:
Objects of different types, except different numeric types and different string types, never compare equal; such objects are ordered consistently but arbitrarily (so that sorting a heterogeneous array yields a consistent result).
You don't want to raise exceptions when sorting a list of differently typed objects.