[pyupgrade] Clarify fix safety docs (UP007, UP045)#25288
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ntBre merged 2 commits intoMay 21, 2026
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The current "Fix safety" sentence ("may lead to runtime errors when
alongside libraries...") obscured which combination of [`target-version`]
and comments actually makes the fix unsafe, and the issue's filer hit
the rule fix on Python 3.10+ (where the fix is safe) and was confused
into thinking the docs implied a stronger warning.
Reword as a single rule + two reasons, in line with @pjonsson's
suggestion of flipping the sentence around: the fix is safe when target
is 3.10+ and there are no comments, otherwise unsafe because (a) pre-3.10
runtime introspection (Pydantic, etc.) can `TypeError` on `X | Y`, or
(b) inline comments would be dropped during rewrite. Applied symmetrically
to UP045's docstring since it had the same phrasing.
Closes astral-sh#17062.
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for future reference, I think the "unusal and likely incorrect" part of this should probably be in a separate Known Issues section, as I don't think this is isolated to Python versions before 3.10, and the code doesn't actually check anything about the types to determine fix safety. astral-sh#9306 added this phrase, which I think is worth having somewhere, just not necessarily in this section
ntBre
changed the title
pyupgrade] Clarify UP007 / UP045 fix safety docspyupgrade] Clarify fix safety docs (UP007, UP045)
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…5288) The current UP007 "Fix safety" paragraph reads "This rule's fix is marked as unsafe, as it may lead to runtime errors when alongside libraries that rely on runtime type annotations, like Pydantic, on Python versions prior to Python 3.10..." The filer of astral-sh#17062 hit the fix on Python 3.10+ (where the source explicitly marks the fix safe) and was confused about what the docs were warning about. In the thread, ntBre clarified the actual semantics ("the fix is marked unsafe on Python versions prior to Python 3.10 but safe on and after 3.10") and pjonsson suggested flipping the sentence around. I rewrote the paragraph to mirror the code: the fix is safe when target is 3.10+ and there are no comments, otherwise it's unsafe for one of two reasons (pre-3.10 runtime introspection like Pydantic can `TypeError` on `X | Y`, or comments inside the original would be dropped during rewrite). The unusual-inner-expression caveat is kept. I applied the same rewrite to UP045's docstring because it had the same wording. Docstring-only. `cargo dev generate-all` and `uvx prek run --from-ref main` both pass. fixes astral-sh#17062 --------- Co-authored-by: Brent Westbrook <brentrwestbrook@gmail.com>
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May 28, 2026
…5288) The current UP007 "Fix safety" paragraph reads "This rule's fix is marked as unsafe, as it may lead to runtime errors when alongside libraries that rely on runtime type annotations, like Pydantic, on Python versions prior to Python 3.10..." The filer of astral-sh#17062 hit the fix on Python 3.10+ (where the source explicitly marks the fix safe) and was confused about what the docs were warning about. In the thread, ntBre clarified the actual semantics ("the fix is marked unsafe on Python versions prior to Python 3.10 but safe on and after 3.10") and pjonsson suggested flipping the sentence around. I rewrote the paragraph to mirror the code: the fix is safe when target is 3.10+ and there are no comments, otherwise it's unsafe for one of two reasons (pre-3.10 runtime introspection like Pydantic can `TypeError` on `X | Y`, or comments inside the original would be dropped during rewrite). The unusual-inner-expression caveat is kept. I applied the same rewrite to UP045's docstring because it had the same wording. Docstring-only. `cargo dev generate-all` and `uvx prek run --from-ref main` both pass. fixes astral-sh#17062 --------- Co-authored-by: Brent Westbrook <brentrwestbrook@gmail.com>
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The current UP007 "Fix safety" paragraph reads "This rule's fix is marked as unsafe, as it may lead to runtime errors when alongside libraries that rely on runtime type annotations, like Pydantic, on Python versions prior to Python 3.10..." The filer of #17062 hit the fix on Python 3.10+ (where the source explicitly marks the fix safe) and was confused about what the docs were warning about.
In the thread, ntBre clarified the actual semantics ("the fix is marked unsafe on Python versions prior to Python 3.10 but safe on and after 3.10") and pjonsson suggested flipping the sentence around. I rewrote the paragraph to mirror the code: the fix is safe when target is 3.10+ and there are no comments, otherwise it's unsafe for one of two reasons (pre-3.10 runtime introspection like Pydantic can
TypeErroronX | Y, or comments inside the original would be dropped during rewrite). The unusual-inner-expression caveat is kept. I applied the same rewrite to UP045's docstring because it had the same wording.Docstring-only.
cargo dev generate-allanduvx prek run --from-ref mainboth pass.fixes #17062