`Tuple[...]` is allowed since 3.11+ (gh-31021)

[sobolevn]

Before TypeVarTuple support was megred, this is what happened when Tuple[...] was used:

Python 3.10.0 (default, Nov 1 2021, 10:24:06) [Clang 11.0.0 (clang-1100.0.33.16)] on darwin
Type "help", "copyright", "credits" or "license" for more information.
>>> from typing import Tuple
>>> Tuple[...]
Traceback (most recent call last):
 File "<stdin>", line 1, in <module>
 File "/Users/sobolev/.pyenv/versions/3.10.0/lib/python3.10/typing.py", line 309, in inner
 return func(*args, **kwds)
 File "/Users/sobolev/.pyenv/versions/3.10.0/lib/python3.10/typing.py", line 1210, in __getitem__
 params = tuple(_type_check(p, msg) for p in params)
 File "/Users/sobolev/.pyenv/versions/3.10.0/lib/python3.10/typing.py", line 1210, in <genexpr>
 params = tuple(_type_check(p, msg) for p in params)
 File "/Users/sobolev/.pyenv/versions/3.10.0/lib/python3.10/typing.py", line 173, in _type_check
 raise TypeError(f"{msg} Got{arg!r:.100}.")
TypeError: Tuple[t0, t1, ...]: each t must be a type. Got Ellipsis.

Since 3.11 it is allowed:

Python 3.12.0a0 (heads/main-dirty:a36235d5c7, Sep 11 2022, 12:23:24) [Clang 11.0.0 (clang-1100.0.33.16)] on darwin
Type "help", "copyright", "credits" or "license" for more information.
>>> from typing import Tuple
>>> Tuple[...]
typing.Tuple[...]

What should we do?

1. Keep this as-is, provide a test that this is allowed (I don't know why anyone would use tuple[...])
2. Make sure that it is still an error with newer version: fix regression and add a test case

In both case I would like to send a PR :)

Related:

• Add support for PEP 646 #87390
• bpo-43224: Implement PEP 646 changes to typing.py #31021

CC @JelleZijlstra and @Fidget-Spinner

[serhiy-storchaka]

Stricter check was removed in bpo-46644, so now Tuple accepts virtually arbitrary arguments:

>>> Tuple[4]
typing.Tuple[4]

I do not think that it is right.

[JelleZijlstra]

Thanks for digging that up. This is an intentional change to make the runtime type system more flexible and less opinionated, so that it is easier to evolve it in the future.