Efficiency of len() and pop() in Python

Question

Why is this Significantly faster with comments? Shouldn\'t a pop, a comparison, and a length check be O(1)? Would that significantly affect the speed?

#! /us         


        

Answer 1

Just to answer part of the question: popping from the end (the right end) of a list takes constant time in CPython, but popping from the left end (.pop(0)) takes time proportional to the length of the list: all the elements in the_list[1:] are physically moved one position to the left.

If you need to delete index position 0 frequently, much better to use an instance of collections.deque. Deques support efficient pushing and popping from both ends.

BTW, when I run the program, I get a clean exception:

...
length of pmarbs = 8306108
Traceback (most recent call last):
  File "xxx.py", line 22, in 
    pmarbs.append(pot2)
MemoryError

That happened to be on a 32-bit Windows box. And it doesn't surprise me ;-)