Incorrect scope of list comprehension variables
apt.shansen at gmail.invalid
Sun Apr 4 20:40:19 EDT 2010
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
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
Obfuscation is not a good goal to go after :)
... p.s: change the ".invalid" to ".com" in email address to reply privately.
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