What is the time complexity of popping elements from list in Python?

I wonder what is the time complexity of pop method of list objects in Python (in CPython particulary). Also does the value of N for list.pop(N) affects the complexity?

Yes, it is O(1) to pop the last element of a Python list, and O(N) to pop an arbitrary element (since the whole rest of the list has to be shifted).

Here's a great article on how Python lists are stored and manipulated: http://effbot.org/zone/python-list.htm

Pop() for the last element ought to be O(1) since you only need to return the element referred to by the last element in the array and update the index of the last element. I would expect pop() for an arbitrary element to be O(N) and require on average N/2 operations since you would need to move any elements beyond the element you are removing one position up in the array of pointers.

It should be O(1) with L.pop(-1), and O(n) with L.pop(0)

see following example:

from timeit import timeit
if __name__ == "__main__":
    L = range(100000)
    print timeit("L.pop(0)",  setup="from __main__ import L", number=10000)
    L = range(100000)
    print timeit("L.pop(-1)", setup="from __main__ import L", number=10000)

>>> 0.291752411828
>>> 0.00161794329896