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

This is compact (aside from consume recipe taken from itertools recipes) and should run at C speed:

import collections
import operator
from itertools import islice, tee


def truncate(iterable, n):
    a, b = tee(iterable)
    consume(b, n)
    return map(operator.itemgetter(0), zip(a, b))


# From itertools recipes
def consume(iterator, n=None):
    "Advance the iterator n-steps ahead. If n is None, consume entirely."
    # Use functions that consume iterators at C speed.
    if n is None:
        # feed the entire iterator into a zero-length deque
        collections.deque(iterator, maxlen=0)
    else:
        # advance to the empty slice starting at position n
        next(islice(iterator, n, n), None)