typing.get_type_hints() raises TypeError for a variable annotated by dataclasses.InitVar #88962

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1. tk0miya commented on Jul 31, 2021

   

   tk0miyamannequin

   on Jul 31, 2021

   MannequinAuthor

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   I found typing.get_type_hints() raises TypeError for a variable annotated by dataclasses.InitVar when lazy annotations evaluation-feature is enabled (a.k.a __future__.annotations).

   $ cat test.py
   from __future__ import annotations
   from dataclasses import dataclass, InitVar
   from typing import get_type_hints
   
   @dataclass
   class Foo:
       attr: InitVar[int]
   
   
   get_type_hints(Foo)
   

   $ python -V
   Python 3.9.6
   $ python test.py
   Traceback (most recent call last):
     File "/Users/tkomiya/work/sphinx/test.py", line 10, in <module>
       get_type_hints(Foo)
     File "/Users/tkomiya/.pyenv/versions/3.9.6/lib/python3.9/typing.py", line 1424, in get_type_hints
       value = _eval_type(value, base_globals, localns)
     File "/Users/tkomiya/.pyenv/versions/3.9.6/lib/python3.9/typing.py", line 290, in _eval_type
       return t._evaluate(globalns, localns, recursive_guard)
     File "/Users/tkomiya/.pyenv/versions/3.9.6/lib/python3.9/typing.py", line 545, in _evaluate
       type_ =_type_check(
     File "/Users/tkomiya/.pyenv/versions/3.9.6/lib/python3.9/typing.py", line 164, in _type_check
       raise TypeError(f"{msg} Got {arg!r:.100}.")
   TypeError: Forward references must evaluate to types. Got dataclasses.InitVar[int].
   

   It goes well if lazy annotations evaluation is disabled.
2. tk0miya

   added

   3.8 (EOL)end of lifeend of life

   3.10 (EOL)end of lifeend of life

   3.9 (EOL)end of lifeend of life

   stdlibStandard Library Python modules in the Lib/ directoryStandard Library Python modules in the Lib/ directory

   on Jul 31, 2021
3. ericvsmith

   assigned

   ericvsmith

   on Aug 2, 2021
4. JelleZijlstra commented on Jan 22, 2022

   

   JelleZijlstra

   on Jan 22, 2022

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   I think this should be fixed in typing.py instead. get_type_hints() should be less strict about what it accepts as a type, so users are free to use annotations in innovative ways.

   Static type checkers should have the job of enforcing that type annotations are valid types.
5. JelleZijlstra commented on Mar 12, 2022

   

   JelleZijlstra

   on Mar 12, 2022

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   This is now fixed in main thanks to bpo-46644:

   >>> get_type_hints(Foo)
   {'attr': dataclasses.InitVar[int]}
   

   We're not backporting that change to the bugfix branches. If we want to fix this issue in 3.10 and 3.9, we'll have to add a __call__ method to InitVar. My inclination is that that's not worth it.

   😕React with 😕1Reacted by Finite State Machine
6. JelleZijlstra

   removed

   3.8 (EOL)end of lifeend of life

   on Mar 12, 2022
7. ericvsmith commented on Mar 12, 2022

   

   ericvsmith

   on Mar 12, 2022

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   I agree it's not worth fixing in 3.9 and 3.10.

   😕React with 😕1Reacted by Finite State Machine
8. JelleZijlstra

   closed this as completedon Mar 12, 2022
9. ezio-melotti

   transferred this issue fromon Apr 10, 2022