Georg Brandl <ge...@python.org> added the comment:
> I also notice that the Grammar in the PEP is more complicated:
> nonlocal_stmt ::=
> "nonlocal" identifier ("," identifier)*
> ["=" (target_list "=")+ expression_list]
> | "nonlocal" identifier augop expression_list
>
> The Grammar in the patch is:
> +global_stmt: 'global' NAME (',' NAME)* [','] ['=' testlist]
> +nonlocal_stmt: 'nonlocal' NAME (',' NAME)* [','] ['=' testlist]
>
> It appears that the PEP is trying to support:
>
> nonlocal x = y = z = 1
> nonlocal a, b = c, d = 1
It also tries to support augmented assignment; however I'm not sure what the
semantics of that should be.
Further, there is an ambiguity if too much freedom is allowed: what about
global x = 1, y
Is it declaring a global "x" and assigning a tuple, or declaring a global "x"
and a global "y"?
> If we're going to support the PEP as written, I think we need to
> modify Global() and Nonlocal() to look exactly like Assign(), but add
> an extra check to verify that all of the expressions in the targets
> are Name, List, or Tuple. You'd probably want to check this at the
> time you are generating the AST, so that you're not stuck with some
> extra state in the compiler traversal about whether you are generating
> code for a Global() or an Assign().
I would not support List or Tuple as targets. Same basic problem as
above, and I don't see a use case.
I see two possibilities for the actual syntax:
1) global *either* supports multiple identifiers, *or* one identifier
and an assignment.
2) global always supports multiple identifiers, each with an optional
assignment; tuples need parentheses.
In both cases, I would keep it simple and not allow multiple targets or
augmented assignment.
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Python tracker <rep...@bugs.python.org>
<http://bugs.python.org/issue4199>
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