python 二进制数相加

def add_binary_nums(x,y):
        max_len = max(len(x), len(y))  

        x = x.zfill(max_len)
        y = y.zfill(max_len)  

        result = ''
        carry =   

        for i in range(max_len-, -, -):
            r = carry
            r +=  if x[i] == '' else
            r +=  if y[i] == '' else
            result = ('' if r %  ==  else '') + result
            carry =  if r <  else          

        if carry != : result = '' + result  

        return result.zfill(max_len)  

print(add_binary_nums('', ''))
print(add_binary_nums('', ''))
print(add_binary_nums('', ''))
print(add_binary_nums('', ''))