I have untabified James' patch, ran the tests on the result, but did not otherwise review it.

There is a not-so-easy-to-find thread on python-dev discussing this issue under subject "Python 2.6.5".

Here is a relevant quote from  Martin v. Löwis:

"""
That would require that Barry actually *can* judge the issue at hand. In
the specific case, I would expect that Barry would defer the specifics
of the Windows issue to Windows experts, and then listen to what they
say.

I'm personally split whether the proposed patch is correct (i.e. whether
asctime really *can* be implemented in a cross-platform manner; any
definite ruling on that would be welcome). In the past, we had rather
taken approaches like disabling runtime assertions "locally"; not sure
whether such approaches would work for asctime as well.

In any case, I feel that the issue is not security-critical at all.
People just don't pass out-of-range values to asctime, but instead
typically pass the result of gmtime/localtime, which will not cause any
problems.
"""