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Fix crash when checking slice expression with step 0 in tuple index #18063

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Oct 29, 2024
Merged

Fix crash when checking slice expression with step 0 in tuple index #18063

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3 changes: 3 additions & 0 deletions mypy/types.py
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Original file line number Diff line number Diff line change
Expand Up @@ -2502,6 +2502,9 @@ def slice(
if fallback is None:
fallback = self.partial_fallback

if stride == 0:
return None

if any(isinstance(t, UnpackType) for t in self.items):
total = len(self.items)
unpack_index = find_unpack_in_list(self.items)
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6 changes: 6 additions & 0 deletions test-data/unit/check-tuples.test
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Expand Up @@ -1438,6 +1438,12 @@ reveal_type(t[x:]) # N: Revealed type is "builtins.tuple[Union[builtins.int, bu
t[y:] # E: Slice index must be an integer, SupportsIndex or None
[builtins fixtures/tuple.pyi]

[case testTupleSliceStepZeroNoCrash]
# This was crashing: https://github.com/python/mypy/issues/18062
# TODO: emit better error when 0 is used for step
()[::0] # E: Ambiguous slice of a variadic tuple
Comment on lines +1443 to +1444
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If #18065 gets merged, this test will change:

Suggested change
# TODO: emit better error when 0 is used for step
()[::0] # E: Ambiguous slice of a variadic tuple
()[::0] # E: Slice step cannot be 0

[builtins fixtures/tuple.pyi]

[case testInferTupleTypeFallbackAgainstInstance]
from typing import TypeVar, Generic, Tuple
T = TypeVar('T')
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