Why is my MergeSort so slow in Python?

Question

I\'m having some troubles understanding this behaviour. I\'m measuring the execution time with the timeit-module and get the following results for 10000 cyc

Answer 1

list.pop(0) pops the first element and has to shift all remaining ones, this is an additional O(n) operation which must not happen.

Also, slicing a list object creates a copy:

left = array[:len(array)/2]
right = array[len(array)/2:]

Which means you're also using O(n * log(n)) memory instead of O(n).

I can't see BubbleSort, but I bet it works in-place, no wonder it's faster.

You need to rewrite it to work in-place. Instead of copying part of original list, pass starting and ending indexes.