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PEP 637: Allow empty starred arguments (GH-1744) 

Co-authored-by: Brandt Bucher <brandtbucher@gmail.com>
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Stefano Borini 2020-12-23 18:43:35 +00:00 committed by GitHub
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@ -290,7 +290,7 @@ example use case 1, where a slice is accepted.
The successful implementation of this PEP will result in the following behavior: The successful implementation of this PEP will result in the following behavior:
1. An empty subscript is still illegal, regardless of context:: 1. An empty subscript is still illegal, regardless of context (see Rejected Ideas)::
obj[] # SyntaxError obj[] # SyntaxError
@ -394,7 +394,7 @@ The successful implementation of this PEP will result in the following behavior:
The following notation equivalence should be honored:: The following notation equivalence should be honored::
obj[*()] obj[*()]
# Error. Equivalent to obj[] # Equivalent to obj[()]
obj[*(), foo=3] obj[*(), foo=3]
# Equivalent to obj[foo=3] # Equivalent to obj[foo=3]
@ -414,7 +414,7 @@ The successful implementation of this PEP will result in the following behavior:
The following notation equivalent should be honored:: The following notation equivalent should be honored::
obj[**{}] obj[**{}]
# Error. Equivalent to obj[] # Equivalent to obj[()]
obj[3, **{}] obj[3, **{}]
# Equivalent to obj[3] # Equivalent to obj[3]
@ -836,7 +836,15 @@ This proposal already established that, in case no positional index is given, th
passed value must be the empty tuple. Allowing for the empty index notation would passed value must be the empty tuple. Allowing for the empty index notation would
make the dictionary type accept it automatically, to insert or refer to the value with make the dictionary type accept it automatically, to insert or refer to the value with
the empty tuple as key. Moreover, a typing notation such as ``Tuple[]`` can easily the empty tuple as key. Moreover, a typing notation such as ``Tuple[]`` can easily
be written as ``Tuple`` without the indexing notation. be written as ``Tuple`` without the indexing notation.
However, subsequent discussion with Brandt Bucher during implementation has revealed
that the case ``obj[]`` would fit a natural evolution for variadic generics, giving
more strength to the above comment. In the end, after a discussion between D'Aprano,
Bucher and the author, we decided to leave the ``obj[]`` notation as a syntax
error for now, and possibly extend the notation with an additional PEP to hold
the equivalence ``obj[]`` as ``obj[()]``.
Sentinel value for no given positional index Sentinel value for no given positional index
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