[Python-Dev] RE: Iteration variables and list comprehensions

[David Beazley]

Greg Ewing writes: 
 > Another advantage of changing both together is that
 > we can continue to describe listcomp semantics in terms
 > of for-loops instead of lambdas.

Is this really an advantage?  To me, the lambda semantics are a lot
more intuitive in terms of matching the way that list comprehensions
are actually used and ought to work (although I will agree that the
for-loop explanation is a good way to describe the internals of what a
list comprehension actually does).

I think I would be opposed to changing normal for-loop semantics to
match any change made in list-comprehensions. There are too many cases
where you use a loop variable after finishing a loop and I suspect
that this would break a huge amount of code. For example:

    for i in r:
        ...
        if whatever: break

    print i

Besides, the semantic mismatch created between a listcomp and a
for-loop pales in comparison to the mismatch that currently exists
between the behavior of listcomps and all of the other operators.  Of
course, that's just my opinion--I could be wrong.

 > Then we won't have to go 
 > into hiding until Guido dies or lifts the fatwah against us.

fatwah?  Uh...  should I start talking to the witness protection
program folks?

Cheers,

Dave