[Tal Einat]
> So we keep things consistent by supporting Decimal and Fraction inputs, but raising ValueError if the value isn't a non-negative integer?

Re-reading the issue comments, my preference is still the same as expressed in msg313936:

- no behaviour change if the input is a float
- if the input is not a float, require it to be integer-like (in the sense of implementing __index__), and complain with a TypeError if it isn't
- defer discussion of deprecating acceptance of integer-valued floats to another issue

So `math.factorial(x)` would become a `TypeError` for a `Decimal` or `Fraction` instance, whether integral or not.