Bug with patch and mypy

[staticdev]

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.

[JelleZijlstra]

I suppose this is caused by #3871?

[staticdev]

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

[srittau]

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.

[staticdev]

@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.

[srittau]

That would be the best solution, of course.

[staticdev]

@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?

[srittau]

@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 ...

[staticdev]

@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.