Paul Ganssle asked me to look at PR 10692. This issue is about consistency, so I don't understand this part of the change:

        try:
            _time.strftime('%')
        except ValueError:
self.skipTest('time module does not support trailing %')

Would why datetime have the same behavior on all platforms, but time.strftime('%') may or may not raise an exception depending on the libc?

Can't we get the same behavior on all platforms and the same behavior in time and datetime module. Honestly, I have no preference between always raising an exception or always success (just copy trailing "%").

This issue reminds me the old bpo-16322: time.strftime("%z") fails to format properly the timezone name. I would suggest to "preprocess" the input string passed to the C function strftime() / wcsftime() to replace %z or %Z with the timezone name, but only pass format substrings?

Something similar can be done for the trailing "%": pass a substring (without the trailing %) to strftime() / wcsftime(), and later append "%".