Fix narrowing with final type objects #20743
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hauntsaninja
commented
Feb 5, 2026
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| if isinstance(typ, UnionType): | ||
| type_ranges = [self.get_type_range_of_type(item) for item in typ.items] | ||
| is_upper_bound = any(t.is_upper_bound for t in type_ranges if t is not None) |
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I added this in https://github.com/python/mypy/pull/20675/files#diff-f96a2d6138bc6cdf2a07c4d37f6071cc25c1631afc107e277a28d5b59fc0ef04R7947 but it's not right, this should always be True
See this test case I mention in the PR description: https://github.com/python/mypy/pull/20675/files#diff-e3de7a75a8a107b4f462b164cdf4945d50505c5e9f7092b753c4add0c01530bbR3021-R3037
for more information, see https://pre-commit.ci
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According to mypy_primer, this change doesn't affect type check results on a corpus of open source code. ✅ |
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Follow up feature request from here: #20675 (comment)
Preserves correct behaviour on this test case: https://github.com/python/mypy/pull/20675/files#diff-e3de7a75a8a107b4f462b164cdf4945d50505c5e9f7092b753c4add0c01530bbR3021-R3037