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Narrow tuples of singletons #21610

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Narrow tuples of singletons
hauntsaninja Jun 8, 2026
d64a7c3
[pre-commit.ci] auto fixes from pre-commit.com hooks
pre-commit-ci[bot] Jun 13, 2026
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9 changes: 8 additions & 1 deletion mypy/typeops.py
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Original file line number Diff line number Diff line change
Expand Up @@ -1071,7 +1071,14 @@ def is_singleton_equality_type(typ: ProperType) -> bool:
Returns True if every value of this type compares equal to every other value of this type,
as judged by the `==` operator.
"""
return isinstance(typ, LiteralType) or is_singleton_identity_type(typ)
return (
isinstance(typ, LiteralType)
or is_singleton_identity_type(typ)
or (
isinstance(typ, TupleType)
and all(is_singleton_equality_type(get_proper_type(t)) for t in typ.items)
)
)


def try_expanding_sum_type_to_union(typ: Type, target_fullname: str | None) -> Type:
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9 changes: 9 additions & 0 deletions test-data/unit/check-narrowing.test
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Expand Up @@ -4281,3 +4281,12 @@ def func(y: H) -> H:
else:
return y
[builtins fixtures/primitives.pyi]

[case testNarrowTupleOfSingletons]
# flags: --strict-equality --warn-unreachable
def f(a: tuple[int, str] | tuple[None, None]):
if a != (None, None):
reveal_type(a) # N: Revealed type is "tuple[builtins.int, builtins.str]"
else:
reveal_type(a) # N: Revealed type is "tuple[None, None]"
[builtins fixtures/primitives.pyi]
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