mypy does not narrow between Generic type[_T] and Callable[[Any], _T]

Bug Report

MyPy doesn't recognize that isinstance(type_var, type) and isinstance(another_var, type_var) narrows another_var to whatever type_var is.

To Reproduce

class RemoteFunction(Generic[_T]):
    def __init__(self, return_type: type[_T] | Callable[[Any], _T]):
        self._return_type = return_type

    def _validate(self, response: Any) -> _T:
        if isinstance(self._return_type, type):
            reveal_type(self._return_type)
            # Revealed type is "builtins.type" Mypy
            # Type of "self._return_type" is "type[object] | type" Pylance
            if not isinstance(response, self._return_type):
                raise TypeError
            reveal_type(response)
            # Revealed type is "builtins.object"Mypy
            # Type of "response" is "Any" Pylance
            return response # Incompatible return value type (got "object", expected "_T")

        return self._return_type(response)

    def __call__(self) -> _T:
        remote_response: Any = None # actually from network/db/etc
        return self._validate(remote_response)

# Usage example
my_remote_func = RemoteFunction(int)
response = my_remote_func()
reveal_type(response)
# Type of "response" is "int" Pylance
# Revealed type is "builtins.int" Mypy

Expected Behavior

mypy should correctly type response as _T

Actual Behavior

test333.py: note: In member "_validate" of class "RemoteFunction":
test333.py:20: note: Revealed type is "builtins.type"
test333.py:25: note: Revealed type is "builtins.object"
test333.py:28: error: Incompatible return value type (got "object", expected "_T")  [return-value]
                return response # Incompatible return value type (got "object", expected "_T")

Interestingly, pyright shows similar types for reveal_type, as annotated above, but does not give an error. Both correctly infer the type of the response in the outer scope, presumably because of the __call__ return type annotation.

Your Environment

• Mypy version used: 1.19.0
• Mypy command-line flags: --strict
• Mypy configuration options from mypy.ini (and other config files):
• Python version used: 3.11.4

Inizia riproducendo l’esempio RemoteFunction con mypy --strict, concentrandoti su _validate, sui controlli isinstance e sui risultati di reveal_type. Traccia come vengono ristrette le variabili di tipo generico quando l’unione contiene type[_T] e Callable[[Any], _T]. Il lavoro è completato quando l’esempio restituisce response come _T senza l’errore di ritorno incompatibile segnalato, preservando al contempo l’inferenza di call esterna.