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#15037·pytest

Acces violation on Windows when importing some scipy modules

Author: schtandardCreated Sep 16, 2026Updated Sep 16, 2026

If I create a folder containing the file test_foo.py with the following content

python
from scipy.special import ellipk
from scipy.optimize import root_scalar

def test_foo():
    assert 1 == 1

and run pytest in that folder twice, I get the following output:

plain
(test) C:\pytest_sandbox>pytest
================================================= test session starts =================================================
platform win32 -- Python 3.14.7, pytest-9.1.1, pluggy-1.6.0
rootdir: C:\pytest_sandbox
collected 1 item

test_foo.py .                                                                                                    [100%]

================================================== 1 passed in 1.08s ==================================================

(test) C:\pytest_sandbox>pytest
================================================= test session starts =================================================
platform win32 -- Python 3.14.7, pytest-9.1.1, pluggy-1.6.0
rootdir: C:\pytest_sandbox
collecting ... Windows fatal exception: access violation

Current thread 0x00000a20 (most recent call first):
  File "<frozen importlib._bootstrap>", line 491 in _call_with_frames_removed
  File "<frozen importlib._bootstrap_external>", line 1053 in create_module
  File "<frozen importlib._bootstrap>", line 816 in module_from_spec
  File "<frozen importlib._bootstrap>", line 924 in _load_unlocked
  File "<frozen importlib._bootstrap>", line 1342 in _find_and_load_unlocked
  File "<frozen importlib._bootstrap>", line 1371 in _find_and_load
  File "<frozen importlib._bootstrap>", line 491 in _call_with_frames_removed
  File "<frozen importlib._bootstrap>", line 1434 in _handle_fromlist
  File "C:\Users\wilde02\AppData\Local\miniforge3\envs\test\Lib\site-packages\scipy\fft\_duccfft\basic.py", line 6 in <module>
  File "<frozen importlib._bootstrap>", line 491 in _call_with_frames_removed
  File "<frozen importlib._bootstrap_external>", line 759 in exec_module
  File "<frozen importlib._bootstrap>", line 938 in _load_unlocked
  File "<frozen importlib._bootstrap>", line 1342 in _find_and_load_unlocked
  File "<frozen importlib._bootstrap>", line 1371 in _find_and_load
  File "C:\Users\wilde02\AppData\Local\miniforge3\envs\test\Lib\site-packages\scipy\fft\_duccfft\__init__.py", line 3 in <module>
  File "<frozen importlib._bootstrap>", line 491 in _call_with_frames_removed
  File "<frozen importlib._bootstrap_external>", line 759 in exec_module
  File "<frozen importlib._bootstrap>", line 938 in _load_unlocked
  File "<frozen importlib._bootstrap>", line 1342 in _find_and_load_unlocked
  File "<frozen importlib._bootstrap>", line 1371 in _find_and_load
  File "C:\Users\wilde02\AppData\Local\miniforge3\envs\test\Lib\site-packages\scipy\fft\_helper.py", line 4 in <module>
  File "<frozen importlib._bootstrap>", line 491 in _call_with_frames_removed
  File "<frozen importlib._bootstrap_external>", line 759 in exec_module
  File "<frozen importlib._bootstrap>", line 938 in _load_unlocked
  File "<frozen importlib._bootstrap>", line 1342 in _find_and_load_unlocked
  File "<frozen importlib._bootstrap>", line 1371 in _find_and_load
  File "C:\Users\wilde02\AppData\Local\miniforge3\envs\test\Lib\site-packages\scipy\fft\__init__.py", line 92 in <module>
  File "<frozen importlib._bootstrap>", line 491 in _call_with_frames_removed
  File "<frozen importlib._bootstrap_external>", line 759 in exec_module
  File "<frozen importlib._bootstrap>", line 938 in _load_unlocked
  File "<frozen importlib._bootstrap>", line 1342 in _find_and_load_unlocked
  File "<frozen importlib._bootstrap>", line 1371 in _find_and_load
  File "<frozen importlib._bootstrap>", line 491 in _call_with_frames_removed
  File "<frozen importlib._bootstrap_external>", line 1061 in exec_module
  File "<frozen importlib._bootstrap>", line 938 in _load_unlocked
  File "<frozen importlib._bootstrap>", line 1342 in _find_and_load_unlocked
  File "<frozen importlib._bootstrap>", line 1371 in _find_and_load
  File "C:\Users\wilde02\AppData\Local\miniforge3\envs\test\Lib\site-packages\scipy\linalg\interpolative.py", line 360 in <module>
  File "<frozen importlib._bootstrap>", line 491 in _call_with_frames_removed
  File "<frozen importlib._bootstrap_external>", line 759 in exec_module
  File "<frozen importlib._bootstrap>", line 938 in _load_unlocked
  File "<frozen importlib._bootstrap>", line 1342 in _find_and_load_unlocked
  File "<frozen importlib._bootstrap>", line 1371 in _find_and_load
  File "C:\Users\wilde02\AppData\Local\miniforge3\envs\test\Lib\site-packages\scipy\optimize\_remove_redundancy.py", line 9 in <module>
  File "<frozen importlib._bootstrap>", line 491 in _call_with_frames_removed
  File "<frozen importlib._bootstrap_external>", line 759 in exec_module
  File "<frozen importlib._bootstrap>", line 938 in _load_unlocked
  File "<frozen importlib._bootstrap>", line 1342 in _find_and_load_unlocked
  File "<frozen importlib._bootstrap>", line 1371 in _find_and_load
  File "C:\Users\wilde02\AppData\Local\miniforge3\envs\test\Lib\site-packages\scipy\optimize\_linprog_util.py", line 9 in <module>
  File "<frozen importlib._bootstrap>", line 491 in _call_with_frames_removed
  File "<frozen importlib._bootstrap_external>", line 759 in exec_module
  File "<frozen importlib._bootstrap>", line 938 in _load_unlocked
  File "<frozen importlib._bootstrap>", line 1342 in _find_and_load_unlocked
  File "<frozen importlib._bootstrap>", line 1371 in _find_and_load
  File "C:\Users\wilde02\AppData\Local\miniforge3\envs\test\Lib\site-packages\scipy\optimize\_linprog_ip.py", line 27 in <module>
  File "<frozen importlib._bootstrap>", line 491 in _call_with_frames_removed
  File "<frozen importlib._bootstrap_external>", line 759 in exec_module
  File "<frozen importlib._bootstrap>", line 938 in _load_unlocked
  File "<frozen importlib._bootstrap>", line 1342 in _find_and_load_unlocked
  File "<frozen importlib._bootstrap>", line 1371 in _find_and_load
  File "C:\Users\wilde02\AppData\Local\miniforge3\envs\test\Lib\site-packages\scipy\optimize\_linprog.py", line 22 in <module>
  File "<frozen importlib._bootstrap>", line 491 in _call_with_frames_removed
  File "<frozen importlib._bootstrap_external>", line 759 in exec_module
  File "<frozen importlib._bootstrap>", line 938 in _load_unlocked
  File "<frozen importlib._bootstrap>", line 1342 in _find_and_load_unlocked
  File "<frozen importlib._bootstrap>", line 1371 in _find_and_load
  File "C:\Users\wilde02\AppData\Local\miniforge3\envs\test\Lib\site-packages\scipy\optimize\__init__.py", line 435 in <module>
  File "<frozen importlib._bootstrap>", line 491 in _call_with_frames_removed
  File "<frozen importlib._bootstrap_external>", line 759 in exec_module
  File "<frozen importlib._bootstrap>", line 938 in _load_unlocked
  File "<frozen importlib._bootstrap>", line 1342 in _find_and_load_unlocked
  File "<frozen importlib._bootstrap>", line 1371 in _find_and_load
  File "C:\pytest_sandbox\test_foo.py", line 2 in <module>
  File "C:\Users\wilde02\AppData\Local\miniforge3\envs\test\Lib\site-packages\_pytest\assertion\rewrite.py", line 188 in exec_module
  File "<frozen importlib._bootstrap>", line 938 in _load_unlocked

Current thread's C stack trace (most recent call first):
  <cannot get C stack on this system>
Windows fatal exception: access violation

Current thread 0x00000a20 (most recent call first):
  File "<frozen importlib._bootstrap>", line 491 in _call_with_frames_removed
  File "<frozen importlib._bootstrap_external>", line 1053 in create_module
  File "<frozen importlib._bootstrap>", line 816 in module_from_spec
  File "<frozen importlib._bootstrap>", line 924 in _load_unlocked
  File "<frozen importlib._bootstrap>", line 1342 in _find_and_load_unlocked
  File "<frozen importlib._bootstrap>", line 1371 in _find_and_load
  File "<frozen importlib._bootstrap>", line 491 in _call_with_frames_removed
  File "<frozen importlib._bootstrap>", line 1434 in _handle_fromlist
  File "C:\Users\wilde02\AppData\Local\miniforge3\envs\test\Lib\site-packages\scipy\fft\_duccfft\basic.py", line 6 in <module>
  File "<frozen importlib._bootstrap>", line 491 in _call_with_frames_removed
  File "<frozen importlib._bootstrap_external>", line 759 in exec_module
  File "<frozen importlib._bootstrap>", line 938 in _load_unlocked
  File "<frozen importlib._bootstrap>", line 1342 in _find_and_load_unlocked
  File "<frozen importlib._bootstrap>", line 1371 in _find_and_load
  File "C:\Users\wilde02\AppData\Local\miniforge3\envs\test\Lib\site-packages\scipy\fft\_duccfft\__init__.py", line 3 in <module>
  File "<frozen importlib._bootstrap>", line 491 in _call_with_frames_removed
  File "<frozen importlib._bootstrap_external>", line 759 in exec_module
  File "<frozen importlib._bootstrap>", line 938 in _load_unlocked
  File "<frozen importlib._bootstrap>", line 1342 in _find_and_load_unlocked
  File "<frozen importlib._bootstrap>", line 1371 in _find_and_load
  File "C:\Users\wilde02\AppData\Local\miniforge3\envs\test\Lib\site-packages\scipy\fft\_helper.py", line 4 in <module>
  File "<frozen importlib._bootstrap>", line 491 in _call_with_frames_removed
  File "<frozen importlib._bootstrap_external>", line 759 in exec_module
  File "<frozen importlib._bootstrap>", line 938 in _load_unlocked
  File "<frozen importlib._bootstrap>", line 1342 in _find_and_load_unlocked
  File "<frozen importlib._bootstrap>", line 1371 in _find_and_load
  File "C:\Users\wilde02\AppData\Local\miniforge3\envs\test\Lib\site-packages\scipy\fft\__init__.py", line 92 in <module>
  File "<frozen importlib._bootstrap>", line 491 in _call_with_frames_removed
  File "<frozen importlib._bootstrap_external>", line 759 in exec_module
  File "<frozen importlib._bootstrap>", line 938 in _load_unlocked
  File "<frozen importlib._bootstrap>", line 1342 in _find_and_load_unlocked
  File "<frozen importlib._bootstrap>", line 1371 in _find_and_load
  File "<frozen importlib._bootstrap>", line 491 in _call_with_frames_removed
  File "<frozen importlib._bootstrap_external>", line 1061 in exec_module
  File "<frozen importlib._bootstrap>", line 938 in _load_unlocked
  File "<frozen importlib._bootstrap>", line 1342 in _find_and_load_unlocked
  File "<frozen importlib._bootstrap>", line 1371 in _find_and_load
  File "C:\Users\wilde02\AppData\Local\miniforge3\envs\test\Lib\site-packages\scipy\linalg\interpolative.py", line 360 in <module>
  File "<frozen importlib._bootstrap>", line 491 in _call_with_frames_removed
  File "<frozen importlib._bootstrap_external>", line 759 in exec_module
  File "<frozen importlib._bootstrap>", line 938 in _load_unlocked
  File "<frozen importlib._bootstrap>", line 1342 in _find_and_load_unlocked
  File "<frozen importlib._bootstrap>", line 1371 in _find_and_load
  File "C:\Users\wilde02\AppData\Local\miniforge3\envs\test\Lib\site-packages\scipy\optimize\_remove_redundancy.py", line 9 in <module>
  File "<frozen importlib._bootstrap>", line 491 in _call_with_frames_removed
  File "<frozen importlib._bootstrap_external>", line 759 in exec_module
  File "<frozen importlib._bootstrap>", line 938 in _load_unlocked
  File "<frozen importlib._bootstrap>", line 1342 in _find_and_load_unlocked
  File "<frozen importlib._bootstrap>", line 1371 in _find_and_load
  File "C:\Users\wilde02\AppData\Local\miniforge3\envs\test\Lib\site-packages\scipy\optimize\_linprog_util.py", line 9 in <module>
  File "<frozen importlib._bootstrap>", line 491 in _call_with_frames_removed
  File "<frozen importlib._bootstrap_external>", line 759 in exec_module
  File "<frozen importlib._bootstrap>", line 938 in _load_unlocked
  File "<frozen importlib._bootstrap>", line 1342 in _find_and_load_unlocked
  File "<frozen importlib._bootstrap>", line 1371 in _find_and_load
  File "C:\Users\wilde02\AppData\Local\miniforge3\envs\test\Lib\site-packages\scipy\optimize\_linprog_ip.py", line 27 in <module>
  File "<frozen importlib._bootstrap>", line 491 in _call_with_frames_removed
  File "<frozen importlib._bootstrap_external>", line 759 in exec_module
  File "<frozen importlib._bootstrap>", line 938 in _load_unlocked
  File "<frozen importlib._bootstrap>", line 1342 in _find_and_load_unlocked
  File "<frozen importlib._bootstrap>", line 1371 in _find_and_load
  File "C:\Users\wilde02\AppData\Local\miniforge3\envs\test\Lib\site-packages\scipy\optimize\_linprog.py", line 22 in <module>
  File "<frozen importlib._bootstrap>", line 491 in _call_with_frames_removed
  File "<frozen importlib._bootstrap_external>", line 759 in exec_module
  File "<frozen importlib._bootstrap>", line 938 in _load_unlocked
  File "<frozen importlib._bootstrap>", line 1342 in _find_and_load_unlocked
  File "<frozen importlib._bootstrap>", line 1371 in _find_and_load
  File "C:\Users\wilde02\AppData\Local\miniforge3\envs\test\Lib\site-packages\scipy\optimize\__init__.py", line 435 in <module>
  File "<frozen importlib._bootstrap>", line 491 in _call_with_frames_removed
  File "<frozen importlib._bootstrap_external>", line 759 in exec_module
  File "<frozen importlib._bootstrap>", line 938 in _load_unlocked
  File "<frozen importlib._bootstrap>", line 1342 in _find_and_load_unlocked
  File "<frozen importlib._bootstrap>", line 1371 in _find_and_load
  File "C:\pytest_sandbox\test_foo.py", line 2 in <module>
  File "C:\Users\wilde02\AppData\Local\miniforge3\envs\test\Lib\site-packages\_pytest\assertion\rewrite.py", line 188 in exec_module
  File "<frozen importlib._bootstrap>", line 938 in _load_unlocked

Current thread's C stack trace (most recent call first):
  <cannot get C stack on this system>
collected 1 item

test_foo.py .                                                                                                    [100%]

================================================== 1 passed in 0.98s ==================================================

That is, the first time it runs without issues, the second time (and all subsequent times) I get an access violation, though the test still passes just fine.

  • If I delete either of the folders .pytest_cache and __pycache__ that are created during the run, the error disappears again (for one run).
  • If I remove either of the two scipy imports, the error disappears immediately.

I have to say that I don't quite understand what's going on here. If you need any more information or debugging done, I'm happy to provide that.

Environment

I am on Windows 11 using a conda environment. pip list reveals the following versions.

plain
(test) C:\pytest_sandbox>pip list
Package           Version
----------------- -------
colorama          0.4.6
exceptiongroup    1.3.1
iniconfig         2.3.0
numpy             2.5.3
packaging         26.3
pip               26.2.1
pluggy            1.6.0
Pygments          2.21.0
pytest            9.1.1
scipy             1.18.1
tomli             2.4.1
typing_extensions 4.16.0
  • a detailed description of the bug or problem you are having
  • output of pip list from the virtual environment you are using
  • pytest and operating system versions
  • minimal example if possible

Source: pytest-dev/pytest

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