Fix Python 3.14 compatiblity #780

thearpankumar · 2025-10-06T12:58:43Z

❓ What kind of change does this PR introduce?

📋 What is the related issue number (starting with #)

Resolves #767

❓ What is the current behavior? (You can also link to an open issue here)

Python 3.14 tests fail in CI with:

Multiprocessing errors due to default start method change from fork to forkserver on Unix
IOBase cleanup errors during test teardown due to changed error message format
Pre-commit failures from flake8-annotations incompatibility

❓ What is the new behavior (if this is a feature change)?

All tests pass on Python 3.14 (Linux and Windows) with full backward compatibility for Python 3.8-3.13.

📋 Other information:

Root Cause: Python 3.14 changed the default multiprocessing start method from fork to forkserver on Unix platforms, breaking pytest-xdist parallel test execution.

Solution Applied:

Multiprocessing Fix (cheroot/test/conftest.py):
- Force fork method on Python 3.14+ Unix systems only
- Skip on Windows (doesn't support fork)
- Clean exception handling with contextlib.suppress
IOBase Warning Filter (pytest.ini):
- Updated regex pattern to match Python 3.14's new error format
- Changed from "Exception ignored in." to "Exception ignored.*"
Pre-commit Config (.pre-commit-config.yaml):
- Set flake8 language_version: python3.11 to match CI
- Prevents flake8-annotations Python 3.14 incompatibility

Testing: Verified on Python 3.14.0rc3 with pytest-xdist parallel execution (n=auto).

📋 Contribution checklist:

This change is

Python 3.14 changed IOBase error message from 'Exception ignored in.' to 'Exception ignored while calling deallocator', breaking the existing regex filter. Updated to match both formats. Also reverted .pre-commit-config.yaml to python3.14 (CI doesn't have 3.13).

… config - Only force 'fork' on Unix (Windows doesn't support fork method) - Change flake8 language_version to python3.11 for CI compatibility - Fixes ValueError on Windows: 'cannot find context for fork'

- Replace try-except-pass with contextlib.suppress (ruff SIM105) - Shorten comment lines to meet 79 char limit (flake8 LN002) - Split nested try blocks to satisfy flake8 WPS229 - Remove unused WPS436 noqa comment

webknjaz · 2025-10-06T14:35:58Z

.pre-commit-config.yaml

    - flake8-spellcheck ~= 0.28.0
    - wemake-python-styleguide ~= 1.1.0
-    language_version: python3.11  # flake8-commas doesn't work w/ Python 3.12
+    # Use Python 3.11 for CI compatibility (flake8-annotations not 3.14 ready)


Why not just update the existing comment. Disconnected comments tend to get lost. Also, it's obvious that Python 3.11 is used from YAML. No need to repeat things too verbosely for the sake of verboseness.

Besides, only the old version is not compatible with Python 3.12. It's unknown if a newer isn't compatible with 3.14. But since there's a release with 3.13 in Trove classifiers, it would make sense to bump the dependency version and maybe bump this to 3.13 if that work + verify if 3.14 could work too.

webknjaz · 2025-10-06T14:38:53Z

cheroot/test/conftest.py

+# Python 3.14 compatibility: Force 'fork' multiprocessing on Unix
+# Python 3.14 changed default from 'fork' to 'forkserver' on Unix,
+# which can cause issues with pytest-xdist's parallel test execution.
+# This ensures compatibility with existing test fixtures and shared state.
+# Note: Windows doesn't support 'fork', so we skip this on Windows.
+# Ref: https://github.com/cherrypy/cheroot/issues/767
+if sys.version_info >= (3, 14) and not IS_WINDOWS:
+    with contextlib.suppress(ImportError):
+        import multiprocessing
+
+        with contextlib.suppress(RuntimeError):
+            # Force fork method even if already set to forkserver
+            multiprocessing.set_start_method('fork', force=True)


This does not seem to have any proof of the justification. Show me fact-checking and actual research. Unnamed possible issues is too broad to make sense of it. Also, post the actual CI failure log (with a link to the line in the log) that this is supposedly addressing.

webknjaz · 2025-10-06T14:39:23Z

cheroot/test/conftest.py

 import pytest

-from .._compat import IS_MACOS, IS_WINDOWS  # noqa: WPS436
+from .._compat import IS_MACOS, IS_WINDOWS


Looks like this is unrelated and can be submitted separately.

webknjaz · 2025-10-06T14:42:36Z

pytest.ini

+  # Python 3.14: PEP 765 - control flow statements in finally blocks
+  # Added as defensive measure even though current code has no violations
+  # Ref: https://github.com/cherrypy/cheroot/issues/767
+  ignore::SyntaxWarning


This must not be ignored. Definitely not as a blanket suppression without justification.

webknjaz · 2025-10-06T14:43:15Z

pytest.ini

+  # Python 3.14 changed error message format from "Exception ignored in." to
+  # "Exception ignored while calling deallocator", so we use a regex that matches both
+  ignore:Exception ignored.*IOBase.__del__:pytest.PytestUnraisableExceptionWarning


Ideally, this should be fixed. But since there was a suppression in place already, It's fine to keep it for now.

webknjaz · 2025-10-06T14:43:56Z

pytest.ini

+  # Python 3.14: Free-threaded build context-aware warnings
+  # Context-aware warnings may behave differently in free-threaded builds
+  # Ref: https://github.com/cherrypy/cheroot/issues/767
+  ignore:.*context.*:RuntimeWarning


This doesn't have any specifics and therefore is not a good/acceptable justification.

thearpankumar and others added 8 commits October 4, 2025 10:08

::CI-run

50ef6df

fix1

a60337f

fix 1

aee66f2

fix 3

a6e4ca0

fix: Add Windows support to multiprocessing fix and update pre-commit…

5570389

… config - Only force 'fork' on Unix (Windows doesn't support fork method) - Change flake8 language_version to python3.11 for CI compatibility - Fixes ValueError on Windows: 'cannot find context for fork'

fix: Use contextlib.suppress and resolve linter violations

7ad5047

- Replace try-except-pass with contextlib.suppress (ruff SIM105) - Shorten comment lines to meet 79 char limit (flake8 LN002) - Split nested try blocks to satisfy flake8 WPS229 - Remove unused WPS436 noqa comment

Merge branch 'main' into fix/python-314-compatiblity

9eb022d

webknjaz changed the title ~~(#767) Fix/python 314 compatiblity~~ Fix Python 3.14 compatiblity Oct 6, 2025

webknjaz reviewed Oct 6, 2025

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Fix Python 3.14 compatiblity #780

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thearpankumar commented Oct 6, 2025 •

edited by webknjaz

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thearpankumar commented Oct 6, 2025 •

edited by webknjaz

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