[8.2.x] fixtures: fix catastrophic performance problem in reorder_items - #12414
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bluetech merged 1 commit intoJun 4, 2024
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[8.2.x] fixtures: fix catastrophic performance problem in reorder_items#12414bluetech merged 1 commit into
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…ems` Manual minimal backport from commit e89d23b. Fix pytest-dev#12355. In the issue, it was reported that the `reorder_items` has quadratic (or worse...) behavior with certain simple parametrizations. After some debugging I found that the problem happens because the "Fix items_by_argkey order" loop keeps adding the same item to the deque, and it reaches epic sizes which causes the slowdown. I don't claim to understand how the `reorder_items` algorithm works, but if as far as I understand, if an item already exists in the deque, the correct thing to do is to move it to the front. Since a deque doesn't have such an (efficient) operation, this switches to `OrderedDict` which can efficiently append from both sides, deduplicate and move to front.
Pierre-Sassoulas
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Jun 4, 2024
webknjaz
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Mar 19, 2025
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src/_pytest/fixtures.py
| for key in argkeys_cache[scope].get(item, []): | ||
| items_by_argkey[scope][key].appendleft(item) | ||
| scoped_items_by_argkey[key][item] = None | ||
| scoped_items_by_argkey[key].move_to_end(item, last=False) |
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Oh.. So this was backported after all. Makes sense given that the regression appeared in v8.2.2.
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webknjaz
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This patch temporarily restricts pytest version below 8.2.2 under PyPy due to a discovered regression that it introduced [[1]]. The regression has been observed on at least `pypy3.9-7.3.16`, `pypy3.10-7.3.19` and `pypy3.11-7.3.19`. It can be triggered by running the following in affected runtimes: pytest --collect-only --no-cov tests/test_abc.py tests/test_copy.py tests/test_incorrect_args.py tests/test_multidict.py tests/test_mypy.py tests/test_pickle.py tests/test_types.py tests/test_update.py tests/test_version.py [1]: pytest-dev/pytest#13312 [2]: pytest-dev/pytest#12414 [3]: pytest-dev/pytest#12409
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Manual minimal backport from commit e89d23b.