Python: Fix cross-type literal matching in pattern comparator#6816
Merged
knutwannheden merged 1 commit intomainfrom Feb 25, 2026
Merged
Python: Fix cross-type literal matching in pattern comparator#6816knutwannheden merged 1 commit intomainfrom
knutwannheden merged 1 commit intomainfrom
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Literal comparison (`_compare_literal`) previously only checked value
equality, which could produce false positives when different literal
types share the same internal representation (e.g., `None`, `...`, and
unicode-escaped strings all store `value=None`).
The fix adds two-level comparison:
1. Reject immediately when value types differ (NoneType vs bytes, etc.)
2. Fall back to `value_source` comparison when both values are `None`
to distinguish `None` from `...` and unicode-escaped literals.
This prevents patterns like `{x} == None` from matching byte string
comparisons like `x == b""`.
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Summary
_compare_literalinPatternMatchingComparatorto prevent cross-type false positivestype(pattern.value) != type(target.value))value_sourcecomparison when both values areNone(disambiguatesNonekeyword from...and unicode-escaped literals which all storevalue=None){x} == Nonefrom incorrectly matching byte string comparisons likex == b""Context
Running
PythonBestPracticesacross 12 open-source projects showedNoneCompareandRemoveNoneFromDefaultGetincorrectly transforming byte string literals:assert response.content == b"Hello"→assert response.content is Nonebody += message.get("body", b"")→body += message.get("body")Test plan
TestCrossTypeLiteralMatching)