Thanks! Unknown kwargs have no effect right? So this would still work for pip<9.0.0?

I'm not sure about unknown kwargs.

I believe it'll have no effect for pip<9.0.0, so perhaps this at the top of setup.py and/or one of the pypinfo/ files should do it.

import sys
if sys.version_info < (3, 5):
    sys.exit('pypinfo requires Python 3.5+')

There's a bigger thing on PLOS/allofplos#20 but perhaps something simpler is fine.