Merge Sort - Python

def merge(arr, left, right):
    i = j = k = 0

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

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

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

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

        merge_sort(left)
        merge_sort(right)

        merge(arr, left, right)

if __name__ == "__main__":
    arr = [12, 11, 13, 5, 6, 7]    
    print("Original Array:", arr)    
    merge_sort(arr)    
    print("Sorted Array:", arr)