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bpo-44589: raise a SyntaxError when mapping patterns have duplicate literal keys (GH-27131)

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Jack DeVries 2021-07-14 20:38:42 -04:00 • committed by GitHub
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4 changed files with 82 additions and 19 deletions
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9
Doc/reference/compound_stmts.rst
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@ -968,9 +968,9 @@ Syntax:
At most one double star pattern may be in a mapping pattern. The double star
pattern must be the last subpattern in the mapping pattern.
Duplicate key values in mapping patterns are disallowed. (If all key patterns
are literal patterns this is considered a syntax error; otherwise this is a
runtime error and will raise :exc:`ValueError`.)
Duplicate keys in mapping patterns are disallowed. Duplicate literal keys will
raise a :exc:`SyntaxError`. Two keys that otherwise have the same value will
raise a :exc:`ValueError` at runtime.
The following is the logical flow for matching a mapping pattern against a
subject value:
@ -982,7 +982,8 @@ subject value:
mapping, the mapping pattern succeeds.
#. If duplicate keys are detected in the mapping pattern, the pattern is
considered invalid and :exc:`ValueError` is raised.
considered invalid. A :exc:`SyntaxError` is raised for duplicate literal
values; or a :exc:`ValueError` for named keys of the same value.
.. note:: Key-value pairs are matched using the two-argument form of the mapping
subject's ``get()`` method. Matched key-value pairs must already be present