> Why not export and use the canonical way of sigemptyset/sigfillset/sigaddset/sigdelset/sigismember instead of pushing for more potential non-conformant code? 

I agree this is the proper fix and that's what I plan to do in Python 3.8.  For Python 3.7 and earlier, though, we cannot add new features anymore, which is why I'm leaning towards a variant of the patch I showed above (which also minimizes the risk for regressions by introducing and using a new API).