[Tutor] list comprehensions isolate variables but for loops don't - is there a special usage?

[Alan Gauld]

On 05/06/13 06:53, Jim Mooney wrote:
> I just noticed that a list comprehension doesn't change a same-name
> variable outside of it, but a for loop does.
>
> For some reason it bothers me that a for loop can do this. Is there a
> simple usage that isolates the for loop iteration variable the way a
> list comprehension does?

No, and it's unlikely to change since a lot of code relies on the fact 
that the for loop iteration variable remembers the last value in the 
loop. This is especially so in loops that have a break exit since its 
useful to know how far through the sequence it got to.

To be honest I didn't realize that comprehensions (and I assume 
generators in general) created their own local namespace. But thinking 
about it, it seems logical since they are effectively functions in 
disguise... Whereas for loops are structures of the language just like 
if statements or while loops. They live in whichever context they are used.

hth
-- 
Alan G
Author of the Learn to Program web site
http://www.alan-g.me.uk/