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extremely slow type checking for constrained <code>TypeVars</code> and overloads on generic classes

performance

Status: Open.

#20439 In python/mypy;

·quczer openedon Dec 18, 2025

detect invalid <code>Literal[Foo.foo | Foo.bar]</code> → <code>Literal[Foo.foo, Foo.bar]</code>

feature

topic-runtime-semanticsmypy doesn't model runtime semantics correctlymypy doesn't model runtime semantics correctly

Status: Open.

#20438 In python/mypy;

·spaceone openedon Dec 18, 2025

Decorator with constrained TypeVar specializes to first constraint

bugmypy got something wrongmypy got something wrong

topic-callsFunction calls, *args, **kwargs, defaultsFunction calls, *args, **kwargs, defaults

Status: Open.

#20437 In python/mypy;

·nkemnitz openedon Dec 18, 2025

type inference failure on custom iterable class unpacking

bugmypy got something wrongmypy got something wrong

Status: Open.

#20435 In python/mypy;

·danmur97 openedon Dec 17, 2025

Return type on enum regression 1.18.2 -&gt; 1.19.0

bugmypy got something wrongmypy got something wrong

topic-enum

topic-inferenceWhen to infer types or require explicit annotationsWhen to infer types or require explicit annotations

topic-type-narrowingConditional type narrowing / binderConditional type narrowing / binder

Status: Open.

#20434 In python/mypy;

·mmiller-max openedon Dec 17, 2025

Setting two arguments to <code>Optional</code> within <code>reveal_type()</code> doesn't get error

bugmypy got something wrongmypy got something wrong

topic-reveal-typereveal_type() and reveal_locals()reveal_type() and reveal_locals()

topic-runtime-semanticsmypy doesn't model runtime semantics correctlymypy doesn't model runtime semantics correctly

Status: Open.

#20432 In python/mypy;

·hyperkai openedon Dec 17, 2025

Regression with <code>UnionType</code> as arg from 1.18.2 to 1.19.0

bugmypy got something wrongmypy got something wrong

Status: Open.

#20426 In python/mypy;

·mmiller-max openedon Dec 16, 2025

False positive error on <code>**kwargs</code> with <code>Mapping[Literal, Any]</code> type

bugmypy got something wrongmypy got something wrong

Status: Open.

#20424 In python/mypy;

·randolf-scholz openedon Dec 16, 2025

list of lists not inferred correctly

feature

topic-inferenceWhen to infer types or require explicit annotationsWhen to infer types or require explicit annotations

topic-join-v-unionUsing join vs. using unionsUsing join vs. using unions

Status: Open.

#20420 In python/mypy;

·Dr-Irv openedon Dec 15, 2025

Errors on @overload in supertype signatures

bugmypy got something wrongmypy got something wrong

Status: Open.

#20418 In python/mypy;

·sveinse openedon Dec 15, 2025

Cannot determine type of walrus operator variable in list comprehension

bugmypy got something wrongmypy got something wrong

topic-callsFunction calls, *args, **kwargs, defaultsFunction calls, *args, **kwargs, defaults

topic-runtime-semanticsmypy doesn't model runtime semantics correctlymypy doesn't model runtime semantics correctly

Status: Open.

#20411 In python/mypy;

·radugheorman openedon Dec 14, 2025

The result of <code>type(TypeVar)</code> is not hashable

bugmypy got something wrongmypy got something wrong

Status: Open.

#20409 In python/mypy;

·arnimarj openedon Dec 13, 2025