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Un-support narrowing final globals in functions #21241

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Merged
ilevkivskyi merged 1 commit into from
Apr 16, 2026
Merged

Un-support narrowing final globals in functions #21241

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Un-support narrowing final globals in functions
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@ilevkivskyi
ilevkivskyi committed Apr 15, 2026
commit 4e7df67864fd0a0483f5ea09c8cc4d5c48d44fc6
4 changes: 0 additions & 4 deletions mypy/checker.py
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Original file line number Diff line number Diff line change
Expand Up @@ -1659,10 +1659,6 @@ 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
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9 changes: 3 additions & 6 deletions test-data/unit/check-final.test
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Expand Up @@ -1238,9 +1238,7 @@ def check_final_init() -> None:
new_instance.__init__()
[builtins fixtures/tuple.pyi]

-- This is tricky and expensive to support in parallel mode.
-- We may want to stop supporting this niche use case
[case testNarrowingOfFinalPersistsInFunctions_no_parallel]
[case testNarrowingOfFinalInFunctionsNotSpecial]
from typing import Final, Union

def _init() -> Union[int, None]:
Expand All @@ -1249,18 +1247,17 @@ def _init() -> Union[int, None]:
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
return FOO # E: Incompatible return value type (got "int | None", expected "int")

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

def func() -> int:
return FOO
return FOO # E: Incompatible return value type (got "int | None", expected "int")

[case testDisjointBase]
from typing_extensions import disjoint_base
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