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| -rw-r--r-- | Doc/reference/expressions.rst | 14 |
1 files changed, 12 insertions, 2 deletions
diff --git a/Doc/reference/expressions.rst b/Doc/reference/expressions.rst index 6bf21a7..edba1c8 100644 --- a/Doc/reference/expressions.rst +++ b/Doc/reference/expressions.rst @@ -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. |