On 2010-04-04 17:01:20 -0700, Steven D'Aprano said:
On Sun, 04 Apr 2010 05:50:01 -0700, Ethan Furman wrote:
Yes, this has been fixed in later revisions, but I'm curious to know
what led you to believe that a list comprehension created a new scope.
I don't that was ever promised.
Common sense about how programming languages should work? As confirmed
by later revisions?
Common sense? About *somebody else's* idea of how a programming
language should work?
Nevertheless, it is a common intuition that the list comp variable should
*not* be exposed outside of the list comp, and that the for-loop variable
should. Perhaps it makes no sense, but it is very common -- I've never
heard of anyone being surprised that the for-loop variable is exposed,
but I've seen many people surprised by the fact that list-comps do expose
their loop variable.
IMHO, the real confusion-point of the situation wasn't so much list
comps vs for loops, but that list comps did expose it, but gen comps
didn't. If one thinks about how each would most likely be implemented
they wouldn't be surprised, but I'm glad the behavior was harmonized in
3.x.
That said, I can't quite imagine how anyone could really sit down and
write code which would be broken by list comps "leaking". The example
code in this thread is just nutty. Even if list comps did create a new
scope, why in the world would you intentionally shadow an enclosing
iteration variable?
Obfuscation is not a good goal to go after :)
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