gh-91803: Mock - fix error when using autospec methods with seal

[akulakov]

• Issue: Can't call mocked methods after create_autospec() and seal() #91803

[carljm]

The fix looks correct to me. "Being callable" is clearly part of the contract of a callable that should be replicated by autospec, and seal should not remove that.

[cjw296]

I'm guessing @sobolevn or @corona10 added this assertion for a reason, perhaps they could comment?

[AlexWaygood]

I think Nikita is largely on a break from open-source stuff right now FYI

[tirkarthi]

I feel this is an incorrect assert since bar2 method is present on Foo and shouldn't raise. Removing the assert statement the AttributeError here asserted is for the exception that return_value is not found due to seal which this PR fixes and not that bar2 is not found.

./python Lib/unittest/test/testmock/testsealable.py
..............EE....
======================================================================
ERROR: test_seal_with_autospec (__main__.TestSealable.test_seal_with_autospec) (spec_set=True)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/home/karthikeyan/stuff/python/cpython/Lib/unittest/test/testmock/testsealable.py", line 215, in test_seal_with_autospec
    foo.bar2()
    ^^^^^^^^^^
  File "/home/karthikeyan/stuff/python/cpython/Lib/unittest/mock.py", line 1108, in __call__
    return self._mock_call(*args, **kwargs)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/karthikeyan/stuff/python/cpython/Lib/unittest/mock.py", line 1112, in _mock_call
    return self._execute_mock_call(*args, **kwargs)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/karthikeyan/stuff/python/cpython/Lib/unittest/mock.py", line 1184, in _execute_mock_call
    return self.return_value
           ^^^^^^^^^^^^^^^^^
  File "/home/karthikeyan/stuff/python/cpython/Lib/unittest/mock.py", line 638, in __getattr__
    raise AttributeError("Mock object has no attribute %r" % name)
    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
AttributeError: Mock object has no attribute 'return_value'

======================================================================
ERROR: test_seal_with_autospec (__main__.TestSealable.test_seal_with_autospec) (spec_set=False)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/home/karthikeyan/stuff/python/cpython/Lib/unittest/test/testmock/testsealable.py", line 215, in test_seal_with_autospec
    foo.bar2()
    ^^^^^^^^^^
  File "/home/karthikeyan/stuff/python/cpython/Lib/unittest/mock.py", line 1108, in __call__
    return self._mock_call(*args, **kwargs)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/karthikeyan/stuff/python/cpython/Lib/unittest/mock.py", line 1112, in _mock_call
    return self._execute_mock_call(*args, **kwargs)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/karthikeyan/stuff/python/cpython/Lib/unittest/mock.py", line 1184, in _execute_mock_call
    return self.return_value
           ^^^^^^^^^^^^^^^^^
  File "/home/karthikeyan/stuff/python/cpython/Lib/unittest/mock.py", line 638, in __getattr__
    raise AttributeError("Mock object has no attribute %r" % name)
    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
AttributeError: Mock object has no attribute 'return_value'

----------------------------------------------------------------------
Ran 19 tests in 0.121s

FAILED (errors=2)

[tirkarthi]

This could use the child_klass to construct the mock object instead of Mock. This can break code that depended on the return value being an instance of child_klass. Example case as below :

from unittest.mock import create_autospec, seal

class Foo:

    def bar(self):
        pass

spec = create_autospec(Foo)
print(spec.bar())
print(len(spec.bar()))

Python 3.10

python3.10 gh92213.py  
<MagicMock name='mock.bar()' id='140499591708000'>
0

With patch

./python gh92213.py
<Mock name='mock.bar()' id='140578691284304'>
Traceback (most recent call last):
  File "/home/karthikeyan/stuff/python/cpython/gh92213.py", line 10, in <module>
    print(len(spec.bar()))
          ^^^^^^^^^^^^^^^
TypeError: object of type 'Mock' has no len()

[akulakov]

That makes sense to me, I used Mock originally because I wasn't sure if MagicMock might "evade" seal() if set explicitly, but I tested it and it does not:

class Foo:
    x = 1
    def foo(self) -> int:
        return 0
foo=Foo()
foo = mock.create_autospec(foo)
foo.foo().x

==> AttributeError: mock.foo().x

I've pushed the update to use child_klass()

[cjw296]

@akulakov - rather than just manually testing this, please can you add a test to the test suite to ensure it doesn't change in the future?

[akulakov]

@cjw296 that makes sense, I've expanded the unit test - thanks for noting this.

[tirkarthi]

Please fix the conflicts in tests. Changes look fine to me.

[akulakov]

@tirkarthi thanks for letting me know, I fixed the conflict.

[tirkarthi]

LGTM. Thanks @akulakov .

[tirkarthi]

cc: @mariocj89

[iritkatriel]

Updated branch to kick off test again.

@tirkarthi - you approved this back in May. Any reason why it was not merged yet?

[akulakov]

Thanks for reviewing @tirkarthi