TypeError tests can check that an implementation raises a correct exception type i.e., it doesn't raise ValueError prematurely on invalid format_string without checking that there is mapping argument.

METH_O does it for CPython. I'm not sure how other implementations might behave.

eric: I'd read http://docs.python.org/devguide/patch.html#preparation but I thought 4 lines are not worth it to change Misc/ACKS. Full pseudonym: Akira Li