gh-115528: Update language reference for PEP 646 #120294
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AlexWaygood
reviewed
Jun 9, 2024
Doc/reference/expressions.rst
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| @@ -1874,7 +1878,7 @@ Expression lists | |||
| single: , (comma); expression list | |||
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| .. productionlist:: python-grammar | |||
| expression_list: `expression` ("," `expression`)* [","] | |||
| expression_list: `starred_expression` ("," `starred_expression`)* [","] | |||
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This is not strictly correct. expression_list according to the grammar is what appears after yield, but def f(): yield *a is a SyntaxError. (However, yield a, *b is legal.)
To recap: the objective is to make starred expressions valid in `subscription`,
which is used for generics: `Generic[...]`, `list[...]`, etc.
What _is_ gramatically valid in such contexts? Seemingly any of the following.
(At least, none of the following throw `SyntaxError` in a 3.12.3 REPL.)
Generic[x]
Generic[*x]
Generic[*x, y]
Generic[y, *x]
Generic[x := 1]
Generic[x := 1, y := 2]
So introducting
flexible_expression: expression | assignment_expression | starred_item
end then switching `subscription` to use `flexible_expression` sorts that.
But then we need to field `yield` - for which any of the following are
apparently valid:
yield x
yield x,
yield x, y
yield *x,
yield *x, *y
Introducing a separate `yield_list` is the simplest way I've been figure out to
do this - separating out the special case of `starred_item ,`.
mrahtz
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All commit authors signed the Contributor License Agreement. |
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Ugh sorry for the spam all - Git mistake. Let me start a fresh PR. |
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📚 Documentation preview 📚: https://cpython-previews--120294.org.readthedocs.build/
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