mergesort.py

def mergesort(l):
    if len(l) > 1:
        mid = len(l) // 2
        left = l[:mid]
        right = l[mid:]

        left = mergesort(left)
        right = mergesort(right)

        i = 0
        j = 0
        k = 0
        while i < len(left) and j < len(right):
            if left[i] < right[j]:
                l[k] = left[i]
                i += 1
            else:
                l[k] = right[j]
                j += 1
            k += 1

        while i < len(left):
            l[k] = left[i]
            i += 1
            k += 1

        while j < len(right):
            l[k] = right[j]
            j += 1
            k += 1
    return l


l = [54, 26, 93, 17, 77, 31, 44, 55, 20]
l = mergesort(l)
print(l)