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gh-115528: Update language reference for PEP 646 (GH-121181)
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 ,`.
(cherry picked from commit
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| .. | ||
| compound_stmts.rst | ||
| datamodel.rst | ||
| executionmodel.rst | ||
| expressions.rst | ||
| grammar.rst | ||
| import.rst | ||
| index.rst | ||
| introduction.rst | ||
| lexical_analysis.rst | ||
| simple_stmts.rst | ||
| toplevel_components.rst | ||