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{"@context":"https://schema.org","@type":"DiscussionForumPosting","headline":"TypeForm: Recognize type variables in a consistent way","articleBody":"\u003e **Prerequisite:** This issue applies after PR https://github.com/python/mypy/pull/19596 is merged.\n\nCurrently mypy sometimes allows a type variable to be assigned to a TypeForm variable and sometimes it does not. This is a problem because the behavior is inconsistent.\n\nSpecifically, mypy allows a type variable to be assigned to a TypeForm variable iff it is in a quoted type expression:\n\n```python\n[case testTypeVarTypeFormsAreOnlyRecognizedInStringAnnotation]\n...\nE = TypeVar('E')\nclass Box(Generic[E]):\n    def foo(self, e: E) -\u003e None:\n        list_of_typx: List[TypeForm] = [E]  # E: \"E\" is a type variable and only valid in type context\n        typx1: TypeForm = E  # E: \"E\" is a type variable and only valid in type context\n        typx2: TypeForm = 'E'\n```\n\nWhen a type variable is NOT quoted, mypy will not allow it to be assigned:\n\n```python\n[case testEveryKindOfTypeExpressionIsAssignableToATypeFormVariable]\nSomeTypeVar = TypeVar('SomeTypeVar')\ntypx: TypeForm\n...\n# NOTE: Unbound TypeVar isn't currently accepted as a TypeForm. Is that OK?\ntypx = SomeTypeVar  # E: Incompatible types in assignment (expression has type \"TypeVar\", variable has type \"TypeForm[Any]\")\n```\n\nI'd argue that TypeForm should always accept a type variable because it is a valid type expression and TypeForms are intended to accept all kinds of type expressions:\n\n```\ndef cast[T](type_expr: TypeForm[T], value_expr: object) -\u003e T: ...\n\ncast(SomeTypeVar, some_expression)  # should not be an error\n```\n\nIn summary:\n* [ ] mypy should allow a type variable to be assigned to a TypeForm variable, regardless of whether it is quoted or not. Update above-referenced tests to reflect this new behavior.","author":{"url":"https://github.com/davidfstr","@type":"Person","name":"davidfstr"},"datePublished":"2025-10-26T18:02:17.000Z","interactionStatistic":{"@type":"InteractionCounter","interactionType":"https://schema.org/CommentAction","userInteractionCount":0},"url":"https://github.com/20124/mypy/issues/20124"}