[ty] Exclude members starting with _abc_ from a protocol interface
#18467
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carljm
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Jun 4, 2025
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Neither mypy nor pyright implement this, and I'm not sure how much the static typing understanding of protocols should be built around implementation details of runtime-checkable protocols.
But I guess this is not likely to hurt compatibility, since such attributes should be unusual. So it seems fine to do this and re-evaluate if it causes any actual issues.
carljm
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* main: [ty] Only consider a type `T` a subtype of a protocol `P` if all of `P`'s members are fully bound on `T` (astral-sh#18466) [ty] Exclude members starting with `_abc_` from a protocol interface (astral-sh#18467) [ty] Add subdiagnostic suggestion to `unresolved-reference` diagnostic when variable exists on `self` (astral-sh#18444) [ty] IDE: only provide declarations and bindings as completions (astral-sh#18456) [ty] ty_ide: Hotfix for `expression_scope_id` panics (astral-sh#18455) [ty] Improve docs for Class{Literal,Type}::instance_member (astral-sh#18454) [ty] Add meta-type tests for legavy TypeVars (astral-sh#18453) update to salsa that doesn't panic silently on cycles (astral-sh#18450)
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Summary
As well as excluding a hardcoded set of special attributes, CPython at runtime also excludes any attributes or declarations starting with
_abc_from the set of members that make up a protocol interface. I missed this in my initial implementation.This is a bit of a CPython implementation detail, but I do think it's important that we try to model the runtime as best we can here. The closer we are to the runtime behaviour, the closer we come to sound behaviour when narrowing types from
isinstance()checks against runtime-checkable protocols (for example)Test Plan
Extended an existing mdtest