Typeshed import cycle causes mypy to start claiming a fixed-length tuple type alias declared with `TypeAlias` is "not valid as a type"

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Evaluación

Dificultad
4/5
Tiempo estimado
3-5 días
Aptitud para principiantes
35/100
Tipo de issue
Error
Claridad
Bastante claro
Estado de actividad
Estancado
Stack tecnológico
python
Área
compilers

Línea de trabajo

Comprueba la rama mypy-import-cycle-repro y ejecuta python tests/mypy_test.py stdlib -p3.12 para reproducir el error en stdlib/zipfile.pyi. Sigue el ciclo de importación a través de los stubs mencionados en el informe, especialmente stdlib/importlib/machinery.pyi, stdlib/importlib/resources/readers.pyi, stdlib/zipfile.pyi, stdlib/typing_extensions.pyi y stdlib/types.pyi; se considera terminado cuando mypy gestiona el ciclo o informa de él de forma inteligible.

Escrito por el modelo de indexación a partir del texto del issue.

Descripción

affects-typeshed bug topic-import-cycles topic-type-alias

Bug Report

We're having a bit of trouble over in https://github.com/python/typeshed/pull/11074. It seems like it's impossible to import importlib.readers inside stdlib/importlib/machinery.pyi and also use typing_extensions.TypeAlias to explicitly demarcate type aliases inside stdlib/zipfile.pyi. The cause appears to be a huge import cycle in our stubs for the standard library:

  • importlib.machinery imports NamespaceReader from importlib.resources.readers
  • importlib.reasources.readers imports zipfile.Path from zipfile
  • zipfile imports TypeAlias from typing_extensions
  • typing_extensions imports get_original_bases from types
  • types imports ModuleSpec from importlib.machinery... and we're back at the beginning.

As a workaround, things seem to work fine for us if we just don't use typing_extensions.TypeAlias for the problematic alias in zipfile.pyi. But this behaviour from mypy seems buggy, so I figured it would be good to file a bug.

To Reproduce

I haven't been able to reproduce this issue outside of the typeshed context. However, I have reduced typeshed down to a "minimum viable typeshed" required to reproduce the bug (https://github.com/AlexWaygood/typeshed/tree/mypy-import-cycle-repro/stdlib). Here are the repro steps:

  1. Clone https://github.com/AlexWaygood/typeshed
  2. Checkout the mypy-import-cycle-repro branch of the repo
  3. Create and activate a venv; run pip install -r requirements-tests.txt
  4. Run python tests/mypy_test.py stdlib -p3.12

Expected Behavior

Mypy handles the import cycle -- or at least gives an intelligible error reporting what the problem is.

Actual Behavior

stdlib\zipfile.pyi:4: error: Variable "zipfile._DateTuple" is not valid as a type  [valid-type]
stdlib\zipfile.pyi:4: note: See https://mypy.readthedocs.io/en/stable/common_issues.html#variables-vs-type-aliases

Your Environment

Lenguaje dominante
Python
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Merge medio
1 d 18 h
PR fusionados (30 d)
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