Positional-only parameters with python 3.10.7 (and numpy) (fixed in 0.981)

[sodul]

Bug Report

After upgrading to python 3.10.7 from 3.10.6 mypy is reporting errors on numpy .pyi files when positional only parameters syntax is present. This error should only get triggered when using versions of python older than 3.8. After rolling back to python 3.10.6 no errors are being reported.

To Reproduce

(Write your steps here:)

1. mypy something_using_numpy.py

Expected Behavior

It should pass without any problem

Actual Behavior

/Users/stephane/.pyenv/versions/3.10.7/lib/python3.10/site-packages/numpy/__init__.pyi:636:48: error: Positional-only parameters are only supported in Python 3.8 and greater  [syntax]
Found 1 error in 1 file (errors prevented further checking)

Your Environment

• mypy==0.971
• Mypy command-line flags: none
• Mypy configuration options:

python_version=3.10
sqlite_cache=True
namespace_packages=True
ignore_missing_imports=True
follow_imports=silent
show_column_numbers=True
check_untyped_defs=True
show_error_codes=True

• Python 3.10.7 (3.10.6 is working fine).
• macOS 12.5.1, Apple CPU
• numpy==1.23.2

[michael-k]

This might be related to

[:func:`ast.parse`](https://github.com/python/cpython/blob/v3.10.7/Misc/NEWS.d/3.10.7.rst#id13)
will no longer parse function definitions with positional-only params when passed feature_version
less than (3, 8). Patch by Shantanu Jain.

Source: https://github.com/python/cpython/blob/v3.10.7/Misc/NEWS.d/3.10.7.rst

Related pull requests/issues:

• issue: ast.parse allows positional-only params with old feature_version cpython#94996
• PR against main: gh-94996: Disallow parsing pos only param with feature_version < (3, 8) cpython#94997
• PR against Python 3.10: [3.10] gh-94996: Disallow parsing pos only params with feature_version < (3, 8) cpython#95935

[michael-k]

Looks like this was already fixed in #13500 (unreleased)

[AlexWaygood]

Yup, a mypy release with the fix will be out soon (might be included in mypy 0.980, if not it will be in mypy 0.990).

Edit: fix was included in 0.981 and newer

[atugushev]

Any known workaround for this?

[AlexWaygood]

Any known workaround for this?

Pin Python to 3.10.6 (not 3.10.7).

[hauntsaninja]

If you're running into this, use mypy 0.981 or newer or downgrade to Python 3.10.6