Can't call mocked methods after create_autospec() and seal()

[dseomn]

Bug report

The code below raises the error below. If I'm understanding the documentation for mock.seal correctly, it's supposed to prevent the creation of new attributes on the sealed mock, not prevent calls to existing methods, right?

from unittest import mock
class Foo:
    def foo(self) -> int:
        return 0
foo = mock.create_autospec(Foo, instance=True)
mock.seal(foo)
foo.foo()

Traceback (most recent call last):
  File "/tmp/tmp.8toUu9Dy3T/foo.py", line 7, in <module>
    foo.foo()
  File "/usr/lib/python3.9/unittest/mock.py", line 1092, in __call__
    return self._mock_call(*args, **kwargs)
  File "/usr/lib/python3.9/unittest/mock.py", line 1096, in _mock_call
    return self._execute_mock_call(*args, **kwargs)
  File "/usr/lib/python3.9/unittest/mock.py", line 1168, in _execute_mock_call
    return self.return_value
  File "/usr/lib/python3.9/unittest/mock.py", line 630, in __getattr__
    raise AttributeError("Mock object has no attribute %r" % name)
AttributeError: Mock object has no attribute 'return_value'

Your environment

• CPython versions tested on: 3.9.9
• Operating system and architecture: Debian testing / amd64

• PR: gh-91803: Mock - fix error when using autospec methods with seal #92213

[eugenetriguba]

If you set the return value beforehand or make a call to that method, you can.

$ ./python
Python 3.11.0a7+ (heads/main:090721721b, Apr 24 2022, 14:58:17) [GCC 11.2.0] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> from unittest import mock
>>> class Foo:
...     def foo(self) -> int:
...         return 0
... 
>>> foo = mock.create_autospec(Foo, instance=True)
>>> foo.foo.return_value = 1
>>> mock.seal(foo)
>>> foo.foo()
1

$ ./python
Python 3.11.0a7+ (heads/main:090721721b, Apr 24 2022, 14:58:17) [GCC 11.2.0] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> from unittest import mock
>>> class Foo:
...     def foo(self) -> int:
...         return 0
... 
>>> foo = mock.create_autospec(Foo, instance=True)
>>> foo.foo()
<MagicMock name='mock.foo()' id='140365640689440'>
>>> mock.seal(foo)
>>> foo.foo()
<MagicMock name='mock.foo()' id='140365640689440'>

This may be related to how mock.create_autospec is creating the mock. For instance:

$ ./python
Python 3.11.0a7+ (heads/main:090721721b, Apr 24 2022, 14:58:17) [GCC 11.2.0] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> from unittest import mock
>>> foo = mock.Mock()
>>> def f(): return 1
... 
>>> f()
1
>>> foo.foo = f
>>> mock.seal(foo)
>>> foo.foo()
1

I'll look into it a little more

[akulakov]

I've added a draft PR #92213 , but I need to work on it a bit more.

[akulakov]

I think the PR may be good, if we consider Mock return value of methods as part of the autospec. That's what such methods return if there is no seal.

However I haven't used seal() before and I haven't used autospec in any advanced way, so I hope this can be looked at by an expert in mock module.