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Callable[[Any], None]" has no attribute "__defaults__" #11896

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Callable[[Any], None]" has no attribute "__defaults__"#11896
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bugmypy got something wrong

Description

@jpy-git
jpy-git
opened on Jan 3, 2022

Bug Report

mypy produces the false positive Callable[[Any], None]" has no attribute "__defaults__" when code uses the __defaults__ attribute of a function.

To Reproduce

Consider this code:

>>> def foo(a) -> None: pass
>>> print(foo.__defaults__)  # None if no default arguments.
None
>>> def bar(a="abc") -> None: pass
>>> print(bar.__defaults__)  # tuple of default arguments.
("abc",)

Run mypy on a script containing this code and get the false-positive:

test.py:2: error: "Callable[[Any], None]" has no attribute "__defaults__"
test.py:4: error: "Callable[[Any], None]" has no attribute "__defaults__"
Found 2 errors in 1 file (checked 1 source file)

Expected Behavior

No mypy errors since it's a valid attribute of a function.

Actual Behavior

mypy errors shown above.

Your Environment

  • Mypy version used: mypy 0.930
  • Mypy command-line flags: N/A
  • Mypy configuration options from mypy.ini (and other config files): N/A
  • Python version used: Python 3.9.9
  • Operating system and version: MacOS Big Sur

Activity

  1. jpy-git
    added
    bugmypy got something wrong
    on Jan 3, 2022

  2. AlexWaygood commented on Jan 3, 2022

    @AlexWaygood
    AlexWaygood
    on Jan 3, 2022
    Member

    It looks to me like the issue is that the definition for the (fictional) function class in typeshed/stdlib/builtins.pyi has not got many of the attributes that the (non-fictional) FunctionType class in typeshed/stdlib/types.pyi has.

    You can get similar mypy errors for the following attributes, which are also defined on types.FunctionType, but not on builtins.function:

    • foo.__closure__
    • foo.__kwdefaults__
    • foo.__get__

  3. jpy-git commented on Jan 3, 2022

    @jpy-git
    jpy-git
    on Jan 3, 2022
    Author

    @AlexWaygood Is there any reason we can't just have builtins.function be a type alias for types.FunctionType since they're the same?
    i.e. function = types.FunctionType

    If not then I'm happy to just copy the attributes over from FuntionType 😄

  4. AlexWaygood commented on Jan 3, 2022

    @AlexWaygood
    AlexWaygood
    on Jan 3, 2022
    Member

    There have been previous attempts to delete builtins.function, which have (sadly) gone badly (see python/typeshed#5799), but I'm not aware of any previous attempts to simply have builtins.function be a type alias for types.FunctionType. Try it, see what happens! 😀

  5. jpy-git commented on Jan 4, 2022

    @jpy-git
    jpy-git
    on Jan 4, 2022
    Author

    Closing as we've fixed this in typeshed 👍

  6. jpy-git
    closed this as completedon Jan 4, 2022
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