[Python-Dev] accumulator display syntax
Guido van Rossum
guido at python.org
Tue Oct 21 17:04:50 EDT 2003
> > ...
> > BTW, while Alex has shown that a generator function with no free
> > variables runs quite fast, a generator expression that uses variables
> > from the surrounding scope will have to use the nested scopes
> > machinery to access those, unlike a list comprehension; not only does
> > this run slower, but it also slows down all other uses of that
> > variable in the surrounding scope (because it becomes a "cell"
> > throughout the scope).
> The implementation could synthesize a generator function abusing default
> arguments to give the generator's frame locals with the same names.
Yes, I think that could work -- I see no way that something invoked by
the generator expression could possibly modify a variable binding in
the surrounding scope.
Argh, someone *could* pass around a copy of locals() and make an
assignment into that. But I think we're already deprecating
non-read-only use of locals(), so I'd like to ban that as abuse.
--Guido van Rossum (home page: http://www.python.org/~guido/)
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