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 = len(lists)/2
left = merge_sort(lists[:middle])
right = merge_sort(lists[middle:])
return merge(left, right)
if __name__ == '__main__': 
= [4, 7, 8, 3, 5, 9]
print merge_sort(a)