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[Python-Dev] PEP 289: Generator Expressions

Guido van Rossum guido at python.org
Thu Oct 23 11:35:56 EDT 2003 
> I'm unclear on the meaning of the last line in detail #3, "(Loop
> variables may also use constructs like x[i] or x.a; this form may be
> deprecated.)"
> 
> Does this mean that "(x.a for x in mylist)" will initiatly be valid but
> will someday break?

No, I meant that "for x.a in mylist: ..." is valid but shouldn't be,
and consequently (because they all share the same syntax) this is also
allowed in list comprehensions and generator expressions.  All uses
should be disallowed.

> If so, I can't imagine why.  Or does in mean that
> the induction variable can be in that form, "(x for x.a in mylist)".
> Surely, this would never be allowed.

We can prevent it for generator expressions, but it's too late for
list comprehensions and regular for loops -- we'll have to go
deprecate it there.

--Guido van Rossum (home page: http://www.python.org/~guido/)
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