[Python-3000] Efficient LC's which don't leak the iteration variables (was Re: Py3k release schedule worries)

[Jim Jewett]

On 12/20/06, Guido van Rossum <guido at python.org> wrote:
> On 12/20/06, Nick Coghlan <ncoghlan at gmail.com> wrote:
> > I haven't actually tried to implement that, though, and I suspect things will
> > get a little tricky when it comes to dealing with nested scopes like '[(lambda
> > i=i: i) for i in range(10)]'.

> That doesn't strike me as tricky; I expect it'll happen automatically
> if you do the right thing.

    [(lambda i=i: i) for i in range(10)]
=>
    [(lambda i=0_i: i) for 0_i in range(10)]

The argument to lambda can't be renamed, because it could be called as
a keyword.

Knowing which i's to rename strikes *me* as tricky, to the point where
I would suggest at least considering a "works as implemented"
pronouncement.  This (along with further nesting, closure variables,
conditionally defined variables, etc) is obscure enough that backwards
incompatibility could be justified, if it made the explanation (or
implementation) simpler.

-jJ