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gh-96397: Document that keywords in calls need not be identifiers (#96393)

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This represents the official SC stance, see
https://github.com/python/steering-council/issues/142#issuecomment-1252172695
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Jeff Allen 2022-09-22 19:10:15 +01:00 • committed by GitHub
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14
Doc/reference/expressions.rst
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@ -1054,10 +1054,20 @@ used in the same call, so in practice this confusion does not often arise.
If the syntax ``**expression`` appears in the function call, ``expression`` must
evaluate to a :term:`mapping`, the contents of which are treated as
additional keyword arguments. If a keyword is already present
(as an explicit keyword argument, or from another unpacking),
additional keyword arguments. If a parameter matching a key has already been
given a value (by an explicit keyword argument, or from another unpacking),
a :exc:`TypeError` exception is raised.
When ``**expression`` is used, each key in this mapping must be
a string.
Each value from the mapping is assigned to the first formal parameter
eligible for keyword assignment whose name is equal to the key.
A key need not be a Python identifier (e.g. ``"max-temp °F"`` is acceptable,
although it will not match any formal parameter that could be declared).
If there is no match to a formal parameter
the key-value pair is collected by the ``**`` parameter, if there is one,
or if there is not, a :exc:`TypeError` exception is raised.
Formal parameters using the syntax ``*identifier`` or ``**identifier`` cannot be
used as positional argument slots or as keyword argument names.