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Merged
hauntsaninja merged 1 commit into from
Oct 21, 2026
Merged

Improve negative narrowing in contains checks #22242

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13 changes: 1 addition & 12 deletions mypy/checker.py
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Original file line number Diff line number Diff line change
Expand Up @@ -6989,16 +6989,6 @@ def comparison_type_narrowing_helper(self, node: ComparisonExpr) -> tuple[TypeMa
all_if_maps = []
all_else_maps = []
for known_item in container_item_types:
# Match the should_coerce_literals logic from narrow_type_by_identity_equality
p_known_item = get_proper_type(known_item)
if (
is_literal_type_like(p_known_item)
or (
isinstance(p_known_item, Instance)
and p_known_item.type.is_enum
)
) and not has_custom_eq_checks(p_known_item):
known_item = coerce_to_literal(known_item)
if_map, else_map = self.narrow_type_by_identity_equality(
"==",
operands=[operands[left_index], operands[right_index]],
Expand All @@ -7007,8 +6997,7 @@ def comparison_type_narrowing_helper(self, node: ComparisonExpr) -> tuple[TypeMa
narrowable_indices={0},
)
all_if_maps.append(if_map)
if is_singleton_equality_type(get_proper_type(known_item)):
all_else_maps.append(else_map)
all_else_maps.append(else_map)
if_map = reduce_or_conditional_type_maps(all_if_maps)
else_map = reduce_and_conditional_type_maps(all_else_maps, use_meet=True)
else:
Expand Down
30 changes: 24 additions & 6 deletions test-data/unit/check-narrowing.test
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Original file line number Diff line number Diff line change
Expand Up @@ -2670,6 +2670,7 @@ def f(x: str | int) -> None:

[case testConsistentNarrowingEqAndInWithCustomEq]
# flags: --strict-equality --warn-unreachable
from typing import Literal

# https://github.com/python/mypy/issues/17864
class C:
Expand All @@ -2689,14 +2690,30 @@ class D(C):
def f1(x: C) -> None:
if x in [D(5)]:
reveal_type(x) # D # N: Revealed type is "__main__.C"
else:
reveal_type(x) # N: Revealed type is "__main__.C"

f1(C(5))

def f2(x: C) -> None:
if x == D(5):
reveal_type(x) # D # N: Revealed type is "__main__.C"
else:
reveal_type(x) # N: Revealed type is "__main__.C"

f2(C(5))

def f3(x: C | Literal[1, 2, 3]) -> None:
if x not in (1, 2):
reveal_type(x) # N: Revealed type is "__main__.C | Literal[3]"
else:
reveal_type(x) # N: Revealed type is "__main__.C | Literal[1] | Literal[2]"

def f4(x: Literal[1, 2], y: C | Literal[1]) -> None:
if x in [y]:
reveal_type(x) # N: Revealed type is "Literal[1] | Literal[2]"
else:
reveal_type(x) # N: Revealed type is "Literal[1] | Literal[2]"
[builtins fixtures/primitives.pyi]

[case testNarrowingTypeVarNone]
Expand Down Expand Up @@ -3251,14 +3268,13 @@ def narrow_tuple_exact(x: Literal['a', 'b', 'c'], t: tuple[Literal['a'], Literal
reveal_type(x) # N: Revealed type is "Literal['a'] | Literal['b']"

def narrow_tuple_expression(x: Literal['a', 'b', 'c']):
# TODO: this should match narrow_tuple_exact
if x in ('a', 'b'):
reveal_type(x) # N: Revealed type is "Literal['a'] | Literal['b']"
else:
reveal_type(x) # N: Revealed type is "Literal['a'] | Literal['b'] | Literal['c']"
reveal_type(x) # N: Revealed type is "Literal['c']"

if x not in ('a', 'b'):
reveal_type(x) # N: Revealed type is "Literal['a'] | Literal['b'] | Literal['c']"
reveal_type(x) # N: Revealed type is "Literal['c']"
else:
reveal_type(x) # N: Revealed type is "Literal['a'] | Literal['b']"

Expand Down Expand Up @@ -3294,7 +3310,7 @@ def narrow_list(x: Literal['a', 'b', 'c'], t: list[Literal['a', 'b']]):
if x in ['a', 'b']:
reveal_type(x) # N: Revealed type is "Literal['a'] | Literal['b']"
else:
reveal_type(x) # N: Revealed type is "Literal['a'] | Literal['b'] | Literal['c']"
reveal_type(x) # N: Revealed type is "Literal['c']"

if x in ['a', 'b', *[]]:
reveal_type(x) # N: Revealed type is "Literal['a'] | Literal['b'] | Literal['c']"
Expand All @@ -3310,7 +3326,7 @@ def narrow_set(x: Literal['a', 'b', 'c'], t: set[Literal['a', 'b']]):
if x in {'a', 'b'}:
reveal_type(x) # N: Revealed type is "Literal['a'] | Literal['b']"
else:
reveal_type(x) # N: Revealed type is "Literal['a'] | Literal['b'] | Literal['c']"
reveal_type(x) # N: Revealed type is "Literal['c']"

if x in {'a', 'b', *[]}:
reveal_type(x) # N: Revealed type is "Literal['a'] | Literal['b'] | Literal['c']"
Expand All @@ -3326,7 +3342,7 @@ def narrow_dict(x: Literal['a', 'b', 'c'], t: dict[Literal['a', 'b'], int]):
if x in {'a': 0, 'b': 1}:
reveal_type(x) # N: Revealed type is "Literal['a'] | Literal['b']"
else:
reveal_type(x) # N: Revealed type is "Literal['a'] | Literal['b'] | Literal['c']"
reveal_type(x) # N: Revealed type is "Literal['c']"

if x in {'a': 0, 'b': 1, **{}}:
reveal_type(x) # N: Revealed type is "Literal['a'] | Literal['b'] | Literal['c']"
Expand All @@ -3350,6 +3366,8 @@ class E(Enum):
def f(x: int) -> None:
if x in [E.foo, E.bar]:
reveal_type(x) # N: Revealed type is "builtins.int"
else:
reveal_type(x) # N: Revealed type is "builtins.int"
[builtins fixtures/list.pyi]


Expand Down
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