fix: handle infinite relative tolerance for timedelta values#14754
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winklemad wants to merge 3 commits into
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fix: handle infinite relative tolerance for timedelta values#14754winklemad wants to merge 3 commits into
winklemad wants to merge 3 commits into
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Pierre-Sassoulas
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Jul 22, 2026
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Thank you for working on this ! I'm curious about what others expect from pytest in this case. Silentely succeed, or raise ? And from their linter ? Probably raise a warning as it's a constant condition or an underhanded way to check typing.
| rel_tolerance = None | ||
| elif math.isinf(rel): | ||
| if expected == timedelta(0): | ||
| raise ValueError("relative tolerance can't be NaN.") |
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Can't be infinite ? Should it be be line 679 with the other sanity guards checks ? This value can be infinite but it doesn't make a lot of sense to test this. (Like an assert True) Maybe warning for this is a linter job and not pytest though.
nicoddemus
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Jul 23, 2026
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Jul 23, 2026
| @@ -0,0 +1 @@ | |||
| ``pytest.approx()`` now rejects infinite relative tolerances for ``datetime.timedelta`` values with a clear ``ValueError`` instead of raising ``OverflowError``. | |||
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I think this should be an improvement rather than a bugfix.
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Summary
pytest.approx()multiplies atimedeltaby the relative tolerance while constructing the comparison. Whenrel=float("inf"), Python raisesOverflowErrorbecausetimedeltahas no infinite representation.Reject infinite relative tolerances alongside the existing negative and NaN validation, producing a clear
ValueErrorbefore multiplication. Numeric approximate-comparison behavior remains unchanged.Validation
tox -e py312 -- testing/python/approx.py::TestApproxDatetime::test_timedelta_rel_must_not_be_infinitetox -e py312 -- testing/python/approx.pytox -e py312tox -e lintinggit diff --check