Bug with patch and mypy

from unittest.mock import Mock
from unittest.mock import patch

import click.testing
import pytest
from pytest_mock import MockFixture

from irpf_cei import __main__

@pytest.fixture
def mock_cei_validate_header(mocker: MockFixture) -> Mock:
    """Fixture for mocking cei.validate."""
    mock = mocker.patch("irpf_cei.cei.validate_header")
    mock.return_value = 2019, "ABC"
    return mock

When I check the code above I get:

error: Returning Any from function declared to return "Mock" 
[no-any-return]
        return mock

But I expect Mock from patch. I worked in previous versions.

I suppose this is caused by #3871?

@JelleZijlstra

@JelleZijlstra is there a release with this fix so I can test?

pytest_mock has no stubs in typeshed, which is why mocker.patch() returns Any. Previously, Mock was aliased to Any, which is why this did not cause errors before. Possible solutions:

Add private stubs for pytest_mock. There are some very basic ones here: https://github.com/srittau/python-stubs/tree/master/stubs/pytest_mock
Use cast(Mock, ...) on the return value.
Use # type: ignore.

@srittau

@srittau so adding type-hints to pytest_mock also solves the problem?
It seems like a more permanent solution and this lib has like 300 lines of code.

That would be the best solution, of course.

@srittau

@srittau while it is not accepted by pytest_mock. I tried adding the stubs for pytest_mock from https://github.com/srittau/python-stubs/tree/master/stubs/pytest_mock.

I am still getting a related errors:

tests/test_validation.py: note: In function "mock_open_valid_file":
tests/test_validation.py:28:5: error: Returning Any from function declared to return "Mock" 
[no-any-return]
        return mocker.patch("builtins.open", mocker.mock_open(read_data="[x]\na = 3"))
        ^
tests/test_validation.py:28:42: error: "MockFixture" has no attribute "mock_open"  [attr-defined]
        return mocker.patch("builtins.open", mocker.mock_open(read_data="[x]\na = 3"))
                                             ^
tests/test_validation.py: note: In function "mock_open_invalid_file":
tests/test_validation.py:34:5: error: Returning Any from function declared to return "Mock" 
[no-any-return]
        return mocker.patch(
        ^
tests/test_validation.py:35:26: error: "MockFixture" has no attribute "mock_open"  [attr-defined]
            "builtins.open", mocker.mock_open(read_data="[x]\na = 3\n[x]\na = 3")
                             ^
Found 4 errors in 1 file (checked 8 source files)

The draft PR is here staticdev/toml-validator#110

Can you also help me with that one?

@staticdev

@staticdev Do you run mypy with MYPYPATH? In our internal codebase, the stubs are in a sub-directory stubs and mypy is called like this: MYPYPATH=stubs mypy ...

@srittau

@srittau yes, I put them on the path. And if I remove the folder I get even more errors:

tests/test_validation.py:5:1: error: Skipping analyzing 'pytest_mock': found module but no type
hints or library stubs  [import]
    from pytest_mock import MockFixture
    ^
tests/test_validation.py: note: In function "mock_tomlkit_parse":
tests/test_validation.py:14:5: error: Returning Any from function declared to return "Mock" 
[no-any-return]
        return mocker.patch("tomlkit.parse")
        ^
tests/test_validation.py: note: In function "mock_tomlkit_parse_exception":
tests/test_validation.py:22:5: error: Returning Any from function declared to return "Mock" 
[no-any-return]
        return mock
        ^
tests/test_validation.py: note: In function "mock_open_valid_file":
tests/test_validation.py:28:5: error: Returning Any from function declared to return "Mock" 
[no-any-return]
        return mocker.patch("builtins.open", mocker.mock_open(read_data="[x]\na = 3"))
        ^
tests/test_validation.py: note: In function "mock_open_invalid_file":
tests/test_validation.py:34:5: error: Returning Any from function declared to return "Mock" 
[no-any-return]
        return mocker.patch(
        ^
tests/test_main.py:6:1: error: Skipping analyzing 'pytest_mock': found module but no type hints or
library stubs  [import]
    from pytest_mock import MockFixture
    ^
tests/test_main.py:6:1: note: See https://mypy.readthedocs.io/en/latest/running_mypy.html#missing-imports
tests/test_main.py: note: In function "mock_validation_validate_extension":
tests/test_main.py:20:5: error: Returning Any from function declared to return "Mock" 
[no-any-return]
        return mocker.patch("toml_validator.validation.validate_extension")
        ^
tests/test_main.py: note: In function "mock_validation_validate_toml_no_error":
tests/test_main.py:28:5: error: Returning Any from function declared to return "Mock" 
[no-any-return]
        return mock
        ^
tests/test_main.py: note: In function "mock_validation_validate_toml_with_error":
tests/test_main.py:36:5: error: Returning Any from function declared to return "Mock" 
[no-any-return]
        return mock
        ^
Found 9 errors in 2 files (checked 8 source files)

I think the argument mocker.mock_open is breaking the interface in this case.

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Bug with patch and mypy #4263

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Bug with patch and mypy #4263

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JelleZijlstra commented on Jun 25, 2020

staticdev commented on Jun 25, 2020

srittau commented on Jun 25, 2020

staticdev commented on Jun 25, 2020

srittau commented on Jun 25, 2020

staticdev commented on Jun 26, 2020

srittau commented on Jun 26, 2020

staticdev commented on Jun 26, 2020

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