8000 patch.dict(x, y) interpreted as invoking __call__, not __init__ · Issue #5118 · python/mypy · GitHub
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patch.dict(x, y) interpreted as invoking __call__, not __init__ #5118

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rbtcollins opened this issue May 29, 2018 · 7 comments
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patch.dict(x, y) interpreted as invoking __call__, not __init__ #5118

rbtcollins opened this issue May 29, 2018 · 7 comments

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@rbtcollins
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rbtcollins commented May 29, 2018 •
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Note: if you are reporting a wrong signature of a function or a class in
the standard library, then the typeshed tracker is better suited
for this report: https://github.com/python/typeshed/issues

I think this is a mypy bug, happy to be sent to typeshed though.

I'm using mypy 0.6, and have the following code:

from unittest import TestCase
from unittest.mock import patch

class A(TestCase):

    @patch.dict("os.environ", {"PATH": os.path.expanduser("~/.local/bin")})
    @patch.object(moduleA, "a")
    @patch("subprocess.check_output")
    def test_missing(self, check_output, a):
        pass

This errors like so:
error: Too many arguments for "__call__" of "_patch_dict"

The typeshed stub for this is

    class _patch_dict:
...
        def __init__(self, in_dict: Any, values: Any = ..., clear: Any = ..., **kwargs: Any) -> None: ...
        def __call__(self, f: Any) -> Any: ...
...

    class _patcher:
        TEST_PREFIX = ...  # type: str
        dict = ...  # type: _patch_dict
...
    patch = ...  # type: _patcher

So mypy should be able to tell that this is instantiating an instance of _patch_dict with __init__ and then that instance is being called with one argument - the curried patcher next inwards in the stack.
@rbtcollins rbtcollins changed the title patch.dict interpreted as __call__ not __init__ patch.dict(x, y) interpreted as invoking __call__, not __init__ May 29, 2018
@li-dan
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li-dan commented May 29, 2018

I think this is a bug in the stubs. patch.dict is the _patch_dict class itself, not an instance of _patch_dict, so the annotation should be # type: Type[_patch_dict], not # type: _patch_dict.

@gvanrossum
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Can one of you submit a PR to typeshed?

@rbtcollins
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Let me give it a spin

@rbtcollins
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Should we also wrap dict in ClassVar ?

@JelleZijlstra
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I think you can just do dict = _patch_dict; haven't tested though.

@rbtcollins
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python/typeshed#2173

@rbtcollins
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@JelleZijlstra you can in Python 3; for some reason that fails on Python 2 (see the typeshed CI job).

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@rbtcollins @JelleZijlstra @gvanrossum @li-dan
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