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merged 2 commits into from
Nov 19, 2024
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Merged

Infer generic type arguments for slice expressions #18160

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cbb91e6
Infer generic type arguments for slice expressions
brianschubert Nov 17, 2024
510455a
Visit index expressions only once
brianschubert Nov 18, 2024
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6 changes: 5 additions & 1 deletion mypy/checkexpr.py
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Original file line number Diff line number Diff line change
Expand Up @@ -5612,11 +5612,15 @@ def visit_slice_expr(self, e: SliceExpr) -> Type:
except KeyError:
supports_index = self.chk.named_type("builtins.int") # thanks, fixture life
expected = make_optional_type(supports_index)
type_args = []
for index in [e.begin_index, e.end_index, e.stride]:
if index:
t = self.accept(index)
self.chk.check_subtype(t, expected, index, message_registry.INVALID_SLICE_INDEX)
return self.named_type("builtins.slice")
type_args.append(t)
else:
type_args.append(NoneType())
return self.chk.named_generic_type("builtins.slice", type_args)

def visit_list_comprehension(self, e: ListComprehension) -> Type:
return self.check_generator_or_comprehension(
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4 changes: 2 additions & 2 deletions test-data/unit/check-expressions.test
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Expand Up @@ -1178,8 +1178,8 @@ class B: pass
[case testSlicingWithInvalidBase]

a: A
a[1:2] # E: Invalid index type "slice" for "A"; expected type "int"
a[:] # E: Invalid index type "slice" for "A"; expected type "int"
a[1:2] # E: Invalid index type "slice[int, int, None]" for "A"; expected type "int"
a[:] # E: Invalid index type "slice[None, None, None]" for "A"; expected type "int"
class A:
def __getitem__(self, n: int) -> 'A': pass
[builtins fixtures/slice.pyi]
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