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Better match narrowing for irrefutable mapping patterns #20906

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Merged
hauntsaninja merged 2 commits into from
Mar 4, 2026
+66 −2
Merged

Better match narrowing for irrefutable mapping patterns #20906

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6e84a67
Better match narrowing for irrefutable mapping patterns
hauntsaninja Feb 25, 2026
b3706b4
Special case Any
hauntsaninja Feb 26, 2026
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Special case Any
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@hauntsaninja
hauntsaninja committed Feb 26, 2026
commit b3706b43381db2347f6e06e11eed558e750152cd
4 changes: 3 additions & 1 deletion mypy/checkpattern.py
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Expand Up @@ -515,12 +515,14 @@ def visit_mapping_pattern(self, o: MappingPattern) -> PatternType:
if not o.keys:
# Match cannot be refuted, so narrow the remaining type
mapping = self.chk.named_type("typing.Mapping")
new_type, else_type = self.chk.conditional_types_with_intersection(
if_type, else_type = self.chk.conditional_types_with_intersection(
current_type,
[TypeRange(mapping, is_upper_bound=False)],
o,
default=current_type,
)
if not isinstance(current_type, AnyType):
new_type = if_type
else:
new_type = UninhabitedType()
return PatternType(new_type, else_type, captures)
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14 changes: 14 additions & 0 deletions test-data/unit/check-python310.test
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Expand Up @@ -660,6 +660,20 @@ def f2_rest(x: Mapping[str, str] | Sequence[str] | str) -> None:
reveal_type(x) # N: Revealed type is "builtins.str"
[builtins fixtures/dict.pyi]

[case testMatchMappingPatternNarrowingAny]
from typing import Any

def f1(x: Any) -> None:
match x:
case {}:
reveal_type(x) # N: Revealed type is "Any"

def f2(x: Any) -> None:
match x:
case {"x": "y"}:
reveal_type(x) # N: Revealed type is "Any"
[builtins fixtures/dict.pyi]

-- Class Pattern --

[case testMatchClassPatternCapturePositional]
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