So this is mostly done... one oddity which may warrant improvement though: signal numbers have multiple names.  ie: SIGABRT is also known as SIGIOT, etc.

This is likely to be confusing to if the error message is surfaced to the user as most users only know one common name rather than all of them as described in their system headers or the signal(7) man page.

I'd rather Python not be in the business of picking which name is more popular, but it can generate different error messages for the same signal across repeated runs due to hash randomization changing the order of the map in the signal.Signals type.

run  python3.5 -c 'import signal; print(signal.Signals(6))'  a handful of times to see this.