```
class Solution(object):
def addBinary(self, a, b):
"""
:type a: str
:type b: str
:rtype: str
"""
if len(a)<len(b):#make a is the longer binary bits
a, b=b, a
b='0'*(len(a)-len(b))+b
carry=0
rst=""
for i in range(len(a)-1, -1, -1):
temp=int(a[i])+int(b[i])+carry
rst=str(temp%2)+rst
carry=temp/2
if carry==1:
rst='1'+rst
return rst
```