I'm re-opening the ticket with a change of subject, because I think this should be treated as a documentation enhancement:

- improve the docstrings for str.isdigit, isnumeric and isdecimal to make it clear what each does (e.g. what counts as a digit);

- similarly improve the documentation for int and float? although the existing comment may be sufficient

https://docs.python.org/3/library/stdtypes.html#numeric-types-int-float-complex

- add a FAQ summarizing the situation.

I don't think we need to worry about backporting the docs to Python 2, but if others disagree, I won't object.