Change return type of ion and ioff to fix unbound variable errors with Pyright
#27667
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I'm confused by how this changes the behavior of pyright: reveal_type(AbstractContextManager.__exit__)Gives: Which still has the Now... emperically, it does not error, I'm just confused why... and worry that it is actually a bug (most likely related to the union return type?) that it does not (and thus will have to do the more complicated fix originally proposed or something like it). |
Pyright currently assumes that errors may be supressed if the return type is either As stated in microsoft/pyright#7009 (comment), the typing rules w.r.t. context managers supressing exceptions have not been formalized (yet), so there is definitely a possibility that at some point in the future the rules change and this fix will no longer work. |
FWIW I checked mypy and mypy also has the same behavior (it assumes errors may be supressed with |
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According to a Pyright maintainer (see microsoft/pyright#7009 (comment)), the current logic for these checks originates from mypy, so we would have to go to mypy maintainers to find out if this is deliberate. I think at this point the pragmatic thing to do is to ship this fix and revisit this if/when things break. I doubt things will change much before the rules of how static analyzers should deal with context managers supressing errors are formalized (see microsoft/pyright#7009 (comment)). |
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This pull request has been open for a while now. Is there anything else I should do to help get this merged, or is it simply a question of waiting? |
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Thanks @FeldrinH! Congratulations on your first PR to Matplotlib 🎉 We hope to hear from you again. |
PR summary
Closes #27659.
By changing the return type annotation to
AbstractContextManager, Pyright considers the context managers returned byionandioffas not supressing errors and does not give warnings about possibly unbound variables after thewithblock.This change has absolutely no effect on runtime behavior.
It might cause type errors for users who store the return value of
ionorioffand attempt to callExitStack-specific methods on it. However, the runtime behavior of such usage has not changed and the number of users who actually do this should be very small, given that the documentation explicitly forbids "storing or accessing" the returned context manager.PR checklist
PS: I couldn't figure out from the developer documentation if changing a type hint constitutes an API change. Let me know if I need to add something to release notes.