May 13, 2025 · May 12, 2025 · May 12, 2025 · May 12, 2025
diff --git a/mypy/checker.py b/mypy/checker.py
        Note that this doesn't do a full CFG analysis but uses a line number based
        heuristic that isn't correct in some (rare) cases.
        """
        if v.is_final:
            # Final vars are definitely never reassigned.
            return False

        outers = self.tscope.outer_functions()
        if not outers:
            # Top-level function -- outer context is top level, and we can't reason about
diff --git a/test-data/unit/check-final.test b/test-data/unit/check-final.test
    new_instance = FinalInit()
    new_instance.__init__()
 [builtins fixtures/tuple.pyi]

 [case testNarrowingOfFinalPersistsInFunctions]
 from typing import Final, Union

 def _init() -> Union[int, None]:
    return 0

 FOO: Final = _init()

 class Example:

    if FOO is not None:
        reveal_type(FOO)  # N: Revealed type is "builtins.int"

        def fn(self) -> int:
            return FOO

 if FOO is not None:
    reveal_type(FOO)  # N: Revealed type is "builtins.int"

    def func() -> int:
        return FOO
Original file line number	Diff line number	Diff line change
Expand Up		@@ -1557,6 +1557,10 @@ def is_var_redefined_in_outer_context(self, v: Var, after_line: int) -> bool:
		Note that this doesn't do a full CFG analysis but uses a line number based
		heuristic that isn't correct in some (rare) cases.
		"""
		if v.is_final:
		# Final vars are definitely never reassigned.
		return False

		outers = self.tscope.outer_functions()
		if not outers:
		# Top-level function -- outer context is top level, and we can't reason about
Expand Down
Original file line number	Diff line number	Diff line change
Expand Up		@@ -1250,3 +1250,25 @@ def check_final_init() -> None:
		new_instance = FinalInit()
		new_instance.__init__()
		[builtins fixtures/tuple.pyi]

		[case testNarrowingOfFinalPersistsInFunctions]
		from typing import Final, Union

		def _init() -> Union[int, None]:
		return 0

		FOO: Final = _init()

		class Example:

		if FOO is not None:
		reveal_type(FOO) # N: Revealed type is "builtins.int"

		def fn(self) -> int:
		return FOO

		if FOO is not None:
		reveal_type(FOO) # N: Revealed type is "builtins.int"

		def func() -> int:
		return FOO