binary addition in python

1#Efficient Binary Addition
2
3def binaryAddEfficient(a, b):
4   if len(a)< len(b):
5      a = (len(b)-len(a))*'0'+a
6   elif len(b)<len(a):
7      b = (len(a)-len(b))*'0'+b
8
9   sumList=[]  #Using a list instead of a string
10   carryover=0
11
12   for i in range(len(a)-1, -1,-1):
13        sum = (int(a[i]) + int(b[i]) +carryover) % 2    
14        carryover = (int(a[i]) + int(b[i]) +carryover) // 2
15        sumList.append(str(sum))  #Appending to the list on the right.
16
17   if carryover:
18        sumList.append(str(carryover))
19
20   sumList.reverse()  #Reverse, because appending gets done on the right.
21   return "".join(sumList)