Loosen Mapping.update() overloads a little
#14593
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Diff from mypy_primer, showing the effect of this PR on open source code: aioredis (https://github.com/aio-libs/aioredis)
+ aioredis/client.py:4116: error: Unused "type: ignore" comment [unused-ignore]
+ aioredis/client.py:4152: error: Unused "type: ignore" comment [unused-ignore]
discord.py (https://github.com/Rapptz/discord.py)
- discord/ext/commands/hybrid.py:508: error: Overlap between argument names and ** TypedDict items: "name", "description" [misc]
+ discord/ext/commands/hybrid.py:508: error: Overlap between argument names and ** TypedDict items: "description", "name" [misc]
- discord/ext/commands/hybrid.py:629: error: Overlap between argument names and ** TypedDict items: "name", "description" [misc]
+ discord/ext/commands/hybrid.py:629: error: Overlap between argument names and ** TypedDict items: "description", "name" [misc]
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Nice -- the |
JelleZijlstra
approved these changes
Aug 19, 2025
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We received a report in ty that said that the changes made in #14099 are now too restrictive. Mypy and ty will now reject a call like this, which feel like it should be valid because
objectis obviously a supertype ofstr:the call is rejected because
Mappingis invariant in its key type, meaning that mypy and ty cannot select this overload:dict[object, object]is not assignable toMapping[str, _VT]:typeshed/stdlib/typing.pyi
Lines 809 to 810 in ab0968b
this PR uses a contravariant protocol for the
selfannotations in theMutableMapping.update()overloads, so that this overload can now be selected if the mapping has a key type that isstror any supertype ofstr. I think this should be sound?Fixes python/mypy#10970, fixes astral-sh/ty#1048