cool-RR wrote: > I'm curious. If I append an item to a list from the left using > `list.insert`, will Python always move the entire list one item to the > right (which can be super-slow) or will it check first to see whether it > can just allocate more memory to the left of the list and put the item > there, saving a lot of resources?
Let's see: $ python3.4 -m timeit -s 'a = [None]' 'a.insert(0, None); del a[0]' 1000000 loops, best of 3: 0.596 usec per loop $ python3.4 -m timeit -s 'a = [None]*1000' 'a.insert(0, None); del a[0]' 100000 loops, best of 3: 2.59 usec per loop $ python3.4 -m timeit -s 'a = [None]*10000' 'a.insert(0, None); del a[0]' 10000 loops, best of 3: 24.7 usec per loop $ python3.4 -m timeit -s 'a = [None]*100000' 'a.insert(0, None); del a[0]' 1000 loops, best of 3: 508 usec per loop $ python3.4 -m timeit -s 'a = [None]*1000000' 'a.insert(0, None); del a[0]' 100 loops, best of 3: 7.61 msec per loop $ python3.4 -m timeit -s 'from collections import deque; a = deque([None]*1000000)' 'a.appendleft(None); a.popleft()' 1000000 loops, best of 3: 0.263 usec per loop -- https://mail.python.org/mailman/listinfo/python-list