No library stub file for standard library module 'typing.re'

[gwk]

from typing.re import Pattern

This is legal, but mypy produces:
`error: No library stub file for standard library module 'typing.re'

[JelleZijlstra]

This seems hard to fix without making typing into a package in the stubs (move typing.pyi to typing/__init__.pyi). That would be rather disruptive though.

[dacut]

Something's amiss here, and I suspect it's in the typing documentation.

The typing documentation only mentions IO, BinaryIO and TextIO in the context of the typing.io wrapper namespace (which is not a module in itself -- it's just a class with class-level variables, IO, BinaryIO, and TextIO). However, these are also defined within the typing module itself, but it is undocumented in the official documentation.

PEP 484 alludes to the existence of this at the typing module level but isn't explicit about it.

Guido may need to weigh in here on the intent, but I'm of the opinion that typing.io should be deprecated (why have a sub-namespace if you're just going to "pollute" the higher-level typing namespace, anyway?), these classes documented in the typing module itself, and leave typeshed as-is.

[gvanrossum]

The intention was actually the opposite -- typing.re.Pattern, typing.io.IO etc. are the proper names, and typing.Pattern etc. are (deprecated?) shortcuts. PEP 484 only mentions typing.re.Pattern etc., and doesn't mention the shortcuts at all.

If the CPython docs don't say this they should be updated.

If we have to turn typing.pyi into typing/__init__.pyi with additional submodules re.pyi and io.pyi so be it. (The typing.py module used at runtime just patches sys.modules, similar to what os.py does for os.path.)

HOWEVER, the reason for the substructure was that typed versions of other stdlib classes could be added as additional submodules of typing. I don't think we're going to do that. So it could be argued that we should reverse course. That would also require amending PEP 484. It's not too late: according to PEP 563, PEP 484 graduates from provisional in 3.8.

[gwk]

Stylistically, I prefer the single flat namespace, e.g. from typing import Pattern, TextIO. I've been using mypy now for about 1.5 years, and compared to other aspects of the system it took me some time to memorize this idiosyncrasy. For people learning the type system, I think it lowers the barrier to entry to flatten these types into a single module and documentation page where they can be browsed and searched for.

[JelleZijlstra]

I'd also prefer supporting just from typing import Pattern for simplicity. Given that from typing.re import Pattern doesn't work with mypy and presumably has never worked, I doubt a lot of users rely on the typing.re and typing.io namespaces.

@gwk @dacut would one of you interested in moving forward this change? It would require amending PEP 484 (as Guido mentioned) as well as the typing documentation in CPython (https://docs.python.org/3/library/typing.html#typing.io) and also making changes in typing.py itself.

[gvanrossum]

OK, let's proceed this way. But I need someone else to take the lead (I'm overwhelmed by small projects already).

[ilevkivskyi]

I don't have time to it all myself, but I can "supervise" if someone volunteers to make actual PRs.

[srittau]

Should this issue be moved over to python/typing?

[srittau]

Moved over to python/typing#589.