3.12.0a7 changes behavior of PropertyMock

[freakboy3742]

Bug report

3.12.0a7 changed the behavior of unittest.mock.PropertyMock

Setup:

from unittest.mock import MagicMock, PropertyMock
m = MagicMock()
p1 = PropertyMock(return_value=3)
p2 = PropertyMock(side_effect=ValueError)
type(m).foo = p1
type(m).bar = p2

In Python 3.12.0a6 and earlier, m.foo evaluates as 3, and m.bar raises a ValueError.

In Python 3.12.0a7, m.foo evaluates as 3, and m.bar returns <MagicMock name='mock.bar' id=...>

Your environment

• CPython versions tested on: 3.12.0a7, 3.12.0a6, 3.11.2, 3.10.10, 3.9.16, 3.8.16
• Operating system and architecture:
  • macOS Ventura 13.2.1, on an M1 MacBook Pro.
  • GitHub Actions macOS 12 x86_64
  • GitHub Actions Ubuntu 22.04
  • GitHub Actions Windows Server 2022

Linked PRs

• gh-103329: Add regression test for PropertyMock with side effect #103358
• [3.11] gh-103329: Add regression test for PropertyMock with side effect (GH-103358) #103364

[sunmy2019]

A known on-going failure was introduced in the related components: aa0a73d

See #103272

Can anyone test if it starts here?

[freakboy3742]

@sunmy2019 I'm not sure aa0a73d is the cause here (or, at least, it isn't the only thing in play); in my testing, that commit still raises a ValueError - although the presentation is slightly different, as it also includes

>>> m.bar
Traceback (most recent call last):
  File "/Users/rkm/projects/python/cpython/github/Lib/unittest/mock.py", line 2957, in __get__
    return self()
           ^^^^^^
  File "/Users/rkm/projects/python/cpython/github/Lib/unittest/mock.py", line 1128, in __call__
    return self._mock_call(*args, **kwargs)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/Users/rkm/projects/python/cpython/github/Lib/unittest/mock.py", line 1132, in _mock_call
    return self._execute_mock_call(*args, **kwargs)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/Users/rkm/projects/python/cpython/github/Lib/unittest/mock.py", line 1187, in _execute_mock_call
    raise effect
ValueError

The above exception was the direct cause of the following exception:

Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/Users/rkm/projects/python/cpython/github/Lib/unittest/mock.py", line 656, in __getattr__
    if name.startswith(('assert', 'assret', 'asert', 'aseert', 'assrt')) or name in _ATTRIB_DENY_LIST:
       ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
SystemError: <method 'startswith' of 'str' objects> returned a result with an exception set

whereas 3.11 et al raise:

Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/Library/Frameworks/Python.framework/Versions/3.11/lib/python3.11/unittest/mock.py", line 2932, in __get__
    return self()
           ^^^^^^
  File "/Library/Frameworks/Python.framework/Versions/3.11/lib/python3.11/unittest/mock.py", line 1118, in __call__
    return self._mock_call(*args, **kwargs)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/Library/Frameworks/Python.framework/Versions/3.11/lib/python3.11/unittest/mock.py", line 1122, in _mock_call
    return self._execute_mock_call(*args, **kwargs)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/Library/Frameworks/Python.framework/Versions/3.11/lib/python3.11/unittest/mock.py", line 1177, in _execute_mock_call
    raise effect
ValueError

[sunmy2019]

Looks like it was fixed by #103332

With current main, I got the same output as in your python3.11. @freakboy3742

[carljm]

Before closing this issue, we should add a test for this case that would have failed on the original breaking PR.

[freakboy3742]

Confirming this has been fixed by #103332. I've submitted some regression tests in #103358.