gh-84978: Add float.from_number() and complex.from_number()

[serhiy-storchaka]

They are alternate constructors which only accept numbers
(including objects with special methods __float__, __complex__
and __index__), but not strings.

https://bugs.python.org/issue40801

• Issue: Expose PyFloat_AsDouble at Python level: operator.as_float? #84978

[github-actions]

This PR is stale because it has been open for 30 days with no activity.

[mdickinson]

@serhiy-storchaka Are you still interested in pursuing this? Looks like it's still a draft; what's needed to make it ready for review?

[serhiy-storchaka]

It needs documentation. I'll write it if the rest be set.

It differs from your original idea (class methods instead of operator functions), so I do not know what you think about this. The spelling is also can be discussed (from_number vs fromnumber, or maybe something other?) Should int.from_number be added?

Should we add also special constructors for parsing? int.parse or int.from_string, etc. It can be done in a different PR, but it is useful to keep it in mind.

[skirpichev]

@serhiy-storchaka, some tests refactoring in test_float/complex is irrelevant for this pr. Can I port this as a separate pr?

[serhiy-storchaka]

This tests refactoring in test_float/complex is required for testing from_number() methods. Without it they are irrelevant. Why do you need this?

[skirpichev]

Why do you need this?

I was thinking about similar refactoring while improving test coverage for the complexobject.c. So, maybe this could be useful regardless of the fate of this pr.

[serhiy-storchaka]

@mdickinson I added docs and remove the draft status. Hope it will help with review.

[mdickinson]

This LGTM, and works as expected in my manual testing. I only have a couple of grammar nitpicks.

Thank you!

[mdickinson]

Super-nitpick: I prefer the spelling floating-point number, with a hyphen (the "floating-point" part acts as a compound adjective). I think that's what we mostly use throughout the docs (though no doubt there are exceptions).

[serhiy-storchaka]

This descriptions was simply copied from the float constructor description.

"floating-point" occurs 118 time, "floating point" occurs at least 159 times (in several cases it is split between lines, so it is not easy to get accurate number).

So for now I leave "floating point" for consistency with the constructor description. We will solve this in a separate issue.