Mergesort algorithm in python

Mergesort algorithm is a divide and conquer algorithm. Its not efficient as Quicksort algorithm but in some cases Mergesort is better than Quicksort. For example if the data to be sorted is in a linked list then Quicksort is costly since in a linkedlist accessing random elements is costly and in Quicksort we have to access data randomly.

Asymptotic Complexity
Something	Time Complexity	Space Complexity
Worst Case Performance	O (n log n)
Best Case Performance	O (n log n )
Average Case Performance	O(n log n)
Worst Case space Complexity		O (n)