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unittest.mock: Regression with create_autospec and dataclasses in 3.14.0b2 #135368

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cdce8p opened this issue Jun 10, 2025 · 6 comments
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unittest.mock: Regression with create_autospec and dataclasses in 3.14.0b2 #135368

cdce8p opened this issue Jun 10, 2025 · 6 comments
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@sobolevn
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topic-dataclasses type-bug An unexpected behavior, bug, or error

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@cdce8p
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cdce8p commented Jun 10, 2025 •
edited by bedevere-app bot
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Bug report

Bug description:

from dataclasses import dataclass
from unittest.mock import create_autospec

@dataclass
class Description:
    name: str

mock = create_autospec(Description, instance=True)
print(isinstance(mock, Description))
# 3.13.3
True

# 3.14.0b2
False

Furthermore the resulting mock doesn't have attributes present on a dataclass instance, like __annotations__, __class__, __dataclass_fields__, __dataclass_params__.

print(dir(mock))
print(dir(Description("Hello World"))

Likely related to #124429. /CC @sobolevn

CPython versions tested on:

3.14

Operating systems tested on:

macOS

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@cdce8p cdce8p added the type-bug An unexpected behavior, bug, or error label Jun 10, 2025
@sobolevn
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cc @ncoghlan and @ericvsmith

@ericvsmith
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As I said on #124429, I'm not a mock user. That said, the regression does seem problematic. @cjw296 is in CODEOWNERS for mock.

@sobolevn
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sobolevn commented Jun 11, 2025 •
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We might need to revert the change, it seems to be rather hard and the fix is not obvious, at least for me now :(

@cjw296
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cjw296 commented Jun 11, 2025

@sobolevn - #124429 was your PR so I hope you can dig into this...

I'd probably tackle this as follows:

  • create new branch from the commit before gh-124176: Add special support for dataclasses to create_autospec #124429 landed, and add tests for isinstance(mock, Description) and the attributes the OP mentions, verifying the past so we basically confirm the PR is the problem
  • rebase the original PR branch (I think GH hangs onto its HEAD commit on the PR even if it was deleted)
  • See what happens with the new tests

If they fail, #124429 should probably be reverted for now, andthe old PR plus new tests put on a branch somewhere that a suitably motivated contributor could pick up.

If a fix can be created, then a new PR should go up containing the additional tests we missed first time round along with the commit for the fix.

Hopefully this all makes sense?

@sobolevn
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Yes, I will surely work on this. If I can find the solution - I will create a PR with the fix. Otherwise, I propose to revert #124429

@sobolevn sobolevn self-assigned this Jun 11, 2025
@cjw296
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cjw296 commented Jun 11, 2025

Start with the missing tests first plz, they'll be a valuable artefact whatever the outcome :-)

@vstinner vstinner changed the title Regression with create_autospec and dataclasses in 3.14.0b2 unittest.mock: Regression with create_autospec and dataclasses in 3.14.0b2 Jun 11, 2025
sobolevn added a commit to sobolevn/cpython that referenced this issue Jun 12, 2025
@sobolevn
pythongh-135368: Fix mocks on dataclass specs with instance=True
e20c6d4
sobolevn added a commit to sobolevn/cpython that referenced this issue Jun 12, 2025
@sobolevn
pythongh-135368: Fix mocks on dataclass specs with instance=True
89b688a
@sobolevn sobolevn mentioned this issue Jun 12, 2025
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@ericvsmith @cjw296 @sobolevn @cdce8p