List as FIFO in for loop

[Roel Schroeven]

malkarouri schreef:
> Hi everyone,
> 
> I have an algorithm in which I need to use a loop over a queue on
> which I push values within the loop, sort of:
> 
> while not(q.empty()):
>     x = q.get()
>     #process x to get zero or more y's
>     #for each y:
>     q.put(y)
> 
> The easiest thing I can do is use a list as a queue and a normal for
> loop:
> 
> q = [a, b, c]
> 
> for x in q:
>     #process x to get zero or more y's
>     q.append(y)
> 
> It makes me feel kind of uncomfortable, though it seems to work. The
> question is: is it guaranteed to work, or does Python expect that you
> wouldn't change the list in the loop?

Changing a loop while iterating over it is to be avoided, if possible. 
In any case, a deque is more efficient for this kind of use. I'd use it 
like this:

from collections import deque

q = deque([a, b, c])
while q:
     x = q.popleft()
     # ...
     q.append(y)

-- 
The saddest aspect of life right now is that science gathers knowledge
faster than society gathers wisdom.
   -- Isaac Asimov

Roel Schroeven