mergesort_arithmetic_python

 def merge(a, b):
     c = []
     h = j = 0
     while j < len(a) and h < len(b):
         if a[j] < b[h]:
             c.append(a[j])
             j += 1
         else:
             c.append(b[h])
             h += 1

     if j == len(a):
         for i in b[h:]:
             c.append(i)
     else:
         for i in a[j:]:
             c.append(i)

     return c

 def merge_sort(lists):
     if len(lists) <= 1:
         return lists
     middle = int(len(lists)/2)
     left = merge_sort(lists[:middle])
     right = merge_sort(lists[middle:])
     return merge(left, right)

 if __name__ == '__main__':
     a = [4, 7, 8, 3, 5, 9]
     print(merge_sort(a))