mergesort.py

class Merge_sort:
    def __call__(self, items):
        return self.sort(items)
        
    def sort(self, items):
        sorted_list = self.sort_helper(items)
        items.clear()
        items.extend(sorted_list)
        return None

    def sort_helper(self, sub_arr):
        if len(sub_arr) <= 1: return sub_arr

        mid = len(sub_arr) // 2
        left =  self.sort_helper(sub_arr[ :mid ])
        right = self.sort_helper(sub_arr[ mid: ])

        return self.merge(left, right)

    def merge(self, left, right):
        sorted_sub_arr = []
        i = 0
        for j in range(len(left)):
            while i < len(right) and right[i] < left[j]:
                sorted_sub_arr.append(right[i])
                i += 1
            sorted_sub_arr.append(left[j])

        if i < len(right): sorted_sub_arr.extend(right[i:])

        return sorted_sub_arr


if __name__ == "__main__":
    
    from random import randint
    
    ms = Merge_sort()

    items = [6, 1, 3, 2, 9, 5, 1, 10, 6, 7, 3, 2, 6, 8, 2, 2, 2, 0, 10, 1]
    print('Original: ' + str(items))
    ms.sort(items)
    print('Sorted:   ' + str(items))
    
    items = [randint(0,10) for x in range(20)]
    print('Original: ' + str(items))
    ms.sort(items)
    print('Sorted:   ' + str(items))

    items = [randint(0,10) for x in range(20)]
    print('Original: ' + str(items))
    ms.sort(items)
    print('Sorted:   ' + str(items))