mergesort.py

# funtion to divide the lists in the two sublists  
def merge_sort(list1, left_index, right_index):  
    if left_index >= right_index:  
        return  
  
    middle = (left_index + right_index)//2  
    merge_sort(list1, left_index, middle)  
    merge_sort(list1, middle + 1, right_index)  
    merge(list1, left_index, right_index, middle)  
  
  
    # Defining a function for merge the list  
def merge(list1, left_index, right_index, middle):  
  
  
   # Creating subparts of a lists  
    left_sublist = list1[left_index:middle + 1]  
    right_sublist = list1[middle+1:right_index+1]  
  
    # Initial values for variables that we use to keep  
    # track of where we are in each list1  
    left_sublist_index = 0  
    right_sublist_index = 0  
    sorted_index = left_index  
  
    # traverse both copies until we get run out one element  
    while left_sublist_index < len(left_sublist) and right_sublist_index < len(right_sublist):  
  
        # If our left_sublist has the smaller element, put it in the sorted  
        # part and then move forward in left_sublist (by increasing the pointer)  
        if left_sublist[left_sublist_index] <= right_sublist[right_sublist_index]:  
            list1[sorted_index] = left_sublist[left_sublist_index]  
            left_sublist_index = left_sublist_index + 1  
        # Otherwise add it into the right sublist  
        else:  
            list1[sorted_index] = right_sublist[right_sublist_index]  
            right_sublist_index = right_sublist_index + 1  
  
  
        # move forward in the sorted part  
        sorted_index = sorted_index + 1  
  
       
    # we will go through the remaining elements and add them  
    while left_sublist_index < len(left_sublist):  
        list1[sorted_index] = left_sublist[left_sublist_index]  
        left_sublist_index = left_sublist_index + 1  
        sorted_index = sorted_index + 1  
  
    while right_sublist_index < len(right_sublist):  
        list1[sorted_index] = right_sublist[right_sublist_index]  
        right_sublist_index = right_sublist_index + 1  
        sorted_index = sorted_index + 1  
  
list1 = [44, 65, 2, 3, 58, 14, 57, 23, 10, 1, 7, 74, 48]  
merge_sort(list1, 0, len(list1) -1)  
print(list1)