There has been some discussion on Python-Ideas about adding fnmatch.filter_false to complement filter, for when you want to ignore matching files rather than non-matching ones.

https://mail.python.org/pipermail/python-ideas/2017-May/045694.html

I don't believe there have been any strong objections, and work-arounds have a considerable performance penalty (according to the OP, I have not confirmed that).

Here's a patch which refactors filter and adds filter_false.

Sorry I haven't got my head around the brave new world on Github, so I'm going old school here with a diff :-)