Use slice notation with collections.deque

Question

How would you extract items 3..6 efficiently, elegantly and pythonically from the following deque without altering it:

from collections import d         


        

Answer 1

This is an old question, but for any future travelers, the Python docs explicitly recommend using rotate for this:

The rotate() method provides a way to implement deque slicing and deletion.

https://docs.python.org/2/library/collections.html

An implementation is relatively simple:

def slice_deque(d, start, stop, step):
    d.rotate(-start)
    slice = list(itertools.islice(d, 0, stop-start, step))
    d.rotate(start)
    return slice

Effectively the same as using islice directly, except that rotate is more efficient for skipping through to the starting point. On the other hand, it also temporarily modifies the deque, which could be a threadsafety concern.