All but the last N elements of iterator in Python

Question

What is the best way to get all but the last N elements of an iterator in Python? Here is an example of it in theoretical action:

>>> list(all_but_         


        

Answer 1

Based on Ignacio Vazquez-Abrams's description:

from collections import deque

def all_but_the_last_n(iterable, count):
    q = deque()
    i = iter(iterable)
    for n in range(count):
        q.append(i.next())
    for item in i:
        q.append(item)
        yield q.popleft()

I wondered whether it was better to use the deque right to left (append, popleft) or left to right (appendleft, pop). So i timed it with python 2.5.2 and found that rtl was 3.59 usec while ltr was 3.53 usec. The difference of 0.06 usec is not significant. the test was to append a single item and pop a single item.