It seems matplotlib now uses the functools32 library on Python 2, which is not needed on Python 3, because functools32 is a backport of Python 3's built in functionality.

This is an issue to us, because we like to compile a list of pinned requirements for Python projects that define the testing environment. Compiling requirements with pip-tools no yields different requirement lists on Python 3 and Python 2. So we would need to now keep track of two lists of requirements, one for Python 3 and one for Python 2 if we want to test with both environments.

Don't really know how this could be optimally addressed, but maybe you could incorporate the lru_cache function directly into your codebase and remove the dependency (since I think lru_cache is the only function used from functools32). Or I could report this to the upstream functools32 because I think one could write functools32 in a backward compatible way so we wouldn't have the issue that we cannot install functools32 on Python 3.