Segfault in Python 3.14.0a5, PyYaml 6.0.3

[skeledrew]

Hello. There seems to be a breaking change in the latest release. Running:

uvx --with pyyaml --python 3.14 --verbose python -X faulthandler -c 'import yaml'

Gives:

DEBUG Searching for Python 3.14 in managed installations or search path
DEBUG Searching for managed installations at `/home/skeledrew/.local/share/uv/python`
DEBUG Found managed installation `cpython-3.14.0a5-linux-x86_64-gnu`
DEBUG Found `cpython-3.14.0a5-linux-x86_64-gnu` at `/home/skeledrew/.local/share/uv/python/cpython-3.14.0a5-linux-x86_64-gnu/bin/python3.14` (managed installations)
DEBUG Acquired lock for `/home/skeledrew/.local/share/uv/tools`
DEBUG Released lock at `/home/skeledrew/.local/share/uv/tools/.lock`
DEBUG Assessing Python executable as base candidate: /home/skeledrew/.local/share/uv/python/cpython-3.14.0a5-linux-x86_64-gnu/bin/python3.14
DEBUG Caching via base interpreter: `/home/skeledrew/.local/share/uv/python/cpython-3.14.0a5-linux-x86_64-gnu/bin/python3.14`
DEBUG Stripping pre-release from `python_full_version`: 3.14.0a5
DEBUG Using request timeout of 30s
DEBUG Solving with installed Python version: 3.14a5
DEBUG Solving with target Python version: >=3.14
DEBUG Adding direct dependency: pyyaml*
DEBUG No cache entry for: https://pypi.org/simple/pyyaml/
WARN Skipping file for pyyaml: PyYAML-3.10.win32-py2.5.exe
WARN Skipping file for pyyaml: PyYAML-3.10.win32-py2.6.exe
WARN Skipping file for pyyaml: PyYAML-3.10.win32-py2.7.exe
WARN Skipping file for pyyaml: PyYAML-3.10.win32-py3.0.exe
WARN Skipping file for pyyaml: PyYAML-3.10.win32-py3.1.exe
WARN Skipping file for pyyaml: PyYAML-3.10.win32-py3.2.exe
WARN Skipping file for pyyaml: PyYAML-3.11.win-amd64-py2.6.exe
WARN Skipping file for pyyaml: PyYAML-3.11.win-amd64-py2.7.exe
WARN Skipping file for pyyaml: PyYAML-3.11.win-amd64-py3.1.exe
WARN Skipping file for pyyaml: PyYAML-3.11.win-amd64-py3.2.exe
WARN Skipping file for pyyaml: PyYAML-3.11.win-amd64-py3.3.exe
WARN Skipping file for pyyaml: PyYAML-3.11.win-amd64-py3.4.exe
WARN Skipping file for pyyaml: PyYAML-3.11.win32-py2.6.exe
WARN Skipping file for pyyaml: PyYAML-3.11.win32-py2.7.exe
WARN Skipping file for pyyaml: PyYAML-3.11.win32-py3.1.exe
WARN Skipping file for pyyaml: PyYAML-3.11.win32-py3.2.exe
WARN Skipping file for pyyaml: PyYAML-3.11.win32-py3.3.exe
WARN Skipping file for pyyaml: PyYAML-3.11.win32-py3.4.exe
WARN Skipping file for pyyaml: PyYAML-3.12.win-amd64-py2.7.exe
WARN Skipping file for pyyaml: PyYAML-3.12.win-amd64-py3.4.exe
WARN Skipping file for pyyaml: PyYAML-3.12.win-amd64-py3.5.exe
WARN Skipping file for pyyaml: PyYAML-3.12.win32-py2.7.exe
WARN Skipping file for pyyaml: PyYAML-3.12.win32-py3.4.exe
WARN Skipping file for pyyaml: PyYAML-3.12.win32-py3.5.exe
WARN Skipping file for pyyaml: PyYAML-4.2b4.win-amd64-py2.7.exe
WARN Skipping file for pyyaml: PyYAML-4.2b4.win-amd64-py3.4.exe
WARN Skipping file for pyyaml: PyYAML-4.2b4.win32-py2.7.exe
WARN Skipping file for pyyaml: PyYAML-4.2b4.win32-py3.4.exe
DEBUG Searching for a compatible version of pyyaml (*)
DEBUG Selecting: pyyaml==6.0.3 [compatible] (pyyaml-6.0.3-cp314-cp314-manylinux2014_x86_64.manylinux_2_17_x86_64.manylinux_2_28_x86_64.whl)
DEBUG No cache entry for: https://files.pythonhosted.org/packages/88/f9/16491d7ed2a919954993e48aa941b200f38040928474c9e85ea9e64222c3/pyyaml-6.0.3-cp314-cp314-manylinux2014_x86_64.manylinux_2_17_x86_64.manylinux_2_28_x86_64.whl.metadata
DEBUG Tried 1 versions: pyyaml 1
DEBUG marker environment resolution took 0.451s
Resolved 1 package in 452ms
DEBUG Assessing Python executable as base candidate: /home/skeledrew/.local/share/uv/python/cpython-3.14.0a5-linux-x86_64-gnu/bin/python3.14
DEBUG Using base executable for virtual environment: /home/skeledrew/.local/share/uv/python/cpython-3.14.0a5-linux-x86_64-gnu/bin/python3.14
DEBUG Ignoring empty directory
DEBUG Using request timeout of 30s
DEBUG Identified uncached distribution: pyyaml==6.0.3
DEBUG No cache entry for: https://files.pythonhosted.org/packages/88/f9/16491d7ed2a919954993e48aa941b200f38040928474c9e85ea9e64222c3/pyyaml-6.0.3-cp314-cp314-manylinux2014_x86_64.manylinux_2_17_x86_64.manylinux_2_28_x86_64.whl
Prepared 1 package in 411ms
Installed 1 package in 3ms
 + pyyaml==6.0.3
DEBUG Checking for Python environment at `/home/skeledrew/.cache/uv/archive-v0/Vok6RbWxkuQZZN0J-Q2M8`
DEBUG Running `python -X faulthandler -c import yaml`
DEBUG Spawned child 2841353 in process group 2841324
Fatal Python error: Segmentation fault

Current thread 0x0000736a343dd740 (most recent call first):
  File "<frozen importlib._bootstrap>", line 488 in _call_with_frames_removed
  File "<frozen importlib._bootstrap_external>", line 1064 in exec_module
  File "<frozen importlib._bootstrap>", line 935 in _load_unlocked
  File "<frozen importlib._bootstrap>", line 1330 in _find_and_load_unlocked
  File "<frozen importlib._bootstrap>", line 1359 in _find_and_load
  File "/home/skeledrew/.cache/uv/archive-v0/Vok6RbWxkuQZZN0J-Q2M8/lib/python3.14/site-packages/yaml/cyaml.py", line 7 in <module>
  File "<frozen importlib._bootstrap>", line 488 in _call_with_frames_removed
  File "<frozen importlib._bootstrap_external>", line 762 in exec_module
  File "<frozen importlib._bootstrap>", line 935 in _load_unlocked
  File "<frozen importlib._bootstrap>", line 1330 in _find_and_load_unlocked
  File "<frozen importlib._bootstrap>", line 1359 in _find_and_load
  File "/home/skeledrew/.cache/uv/archive-v0/Vok6RbWxkuQZZN0J-Q2M8/lib/python3.14/site-packages/yaml/__init__.py", line 13 in <module>
  File "<frozen importlib._bootstrap>", line 488 in _call_with_frames_removed
  File "<frozen importlib._bootstrap_external>", line 762 in exec_module
  File "<frozen importlib._bootstrap>", line 935 in _load_unlocked
  File "<frozen importlib._bootstrap>", line 1330 in _find_and_load_unlocked
  File "<frozen importlib._bootstrap>", line 1359 in _find_and_load
  File "<string>", line 1 in <module>

Extension modules: yaml._yaml (total: 1)
DEBUG Command exited with signal: Some(11)```

Specifying pyyaml==6.0.1 resolves the problem.