Permit either __aenter__ or __aexit__ without checkpoints#444
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Zac-HD merged 3 commits intopython-trio:mainfrom Apr 21, 2026
Merged
Permit either __aenter__ or __aexit__ without checkpoints#444Zac-HD merged 3 commits intopython-trio:mainfrom
__aenter__ or __aexit__ without checkpoints#444Zac-HD merged 3 commits intopython-trio:mainfrom
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ASYNC910 and ASYNC911 no longer require every `__aenter__`/`__aexit__` to contain a checkpoint. Per Trio's documentation, an async context manager only needs one of entry/exit to act as a checkpoint. When a class defines both methods, the one without an `await` is exempt if its partner contains one. When a class defines only one of the two, the partner is charitably assumed to be inherited from a base class and to contain a checkpoint, so the defined method is also exempt. Closes python-trio#441 https://claude.ai/code/session_014jAydKywq31Ew4fVYGJdiG
Two refinements in response to review feedback: - If an `__aenter__`/`__aexit__` method contains any checkpoint-like construct (`await`, `async with`, or `async for`), it must always checkpoint. We no longer exempt such methods even when the partner provides a checkpoint -- conditional checkpoints are still flagged. - Only charitably assume a missing partner is inherited (with a checkpoint) when the class actually inherits from something. Classes with no base classes are treated as flat, and methods that don't checkpoint are flagged. `metaclass=` and other keyword arguments do not count as inheriting, since they live in `ClassDef.keywords` rather than `ClassDef.bases`. https://claude.ai/code/session_014jAydKywq31Ew4fVYGJdiG
When both `__aenter__` and `__aexit__` are defined and neither contains a checkpoint, we used to flag (and autofix) both methods, which produced redundant `lowlevel.checkpoint()` calls -- only one is needed for the async context manager to checkpoint. Prefer to report and fix `__aenter__` in this case; `__aexit__` is exempted since adding a checkpoint to either satisfies the rule. https://claude.ai/code/session_014jAydKywq31Ew4fVYGJdiG
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Fixes #441.