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Fix #19507 Prevent final reassignment in match case #19496

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Merged
merged 1 commit into from
Jul 27, 2025
Merged

Fix #19507 Prevent final reassignment in match case #19496

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2 changes: 2 additions & 0 deletions mypy/checker.py
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Original file line number Diff line number Diff line change
Expand Up @@ -5577,6 +5577,8 @@ def infer_variable_types_from_type_maps(
previous_type, _, _ = self.check_lvalue(expr)
if previous_type is not None:
already_exists = True
if isinstance(expr.node, Var) and expr.node.is_final:
self.msg.cant_assign_to_final(expr.name, False, expr)
if self.check_subtype(
typ,
previous_type,
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10 changes: 10 additions & 0 deletions test-data/unit/check-python310.test
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Expand Up @@ -2839,3 +2839,13 @@ match value_type:
case _:
assert_never(value_type)
[builtins fixtures/tuple.pyi]

[case testAssignmentToFinalInMatchCaseNotAllowed]
from typing import Final

FOO: Final[int] = 10

val: int = 8
match val:
case FOO: # E: Cannot assign to final name "FOO"
pass