py3: minor fix to sage.categories.additive_magmas

[embray]

Replace __nonzero__ with __bool__ for Python 3.

On Python 2 alias __bool__ back to __nonzero__ and delete __bool__.
This allows SageObject._test_not_implemented_methods to pass on Python 2 and 3 for classes that implement this abstract interface.

This could just as easily be done the other way around and I'm not overly particular about it--I just prefer __bool__ for its clearer name.

Component: python3

Author: Erik Bray

Branch/Commit: c84bbe1

Reviewer: Jeroen Demeyer

Issue created by migration from https://trac.sagemath.org/ticket/24294

[jdemeyer]

comment:2

Is there anything wrong with just doing

__nonzero__ = __bool__

unconditionally (as we do in many places in Sage)?

What you are doing here seems like needless complexity...

[embray]

comment:3

Yes, in this specific case. Again it has to do with the SageObject._test_not_implemented_methods. It loops over an object's dir() and in this case may find a __nonzero__ that's not implemented.

[jdemeyer]

comment:4

OK, let it be.

[jdemeyer]

Reviewer: Jeroen Demeyer

[vbraun]

Changed branch from u/embray/python3/additive-magmas-bool to c84bbe1