code

def add_bitwise(b1,b2):

    rest1 = b1[:-1]
    rest2 = b2[:-1}
    if b1 == '' and b2 == '':
        return ''
    elif b1 == '':
        return b2
    elif b2 == '':
        return b1
    else:
        if b1[-1] == '1' and b2[-1] == '0'
            return add_ bitwise(rest1, rest2) + '1'
        elif b1[-1] == '0' and b2[-1] == '1'
            return add_ bitwise(rest1, rest2) + '1'
        elif b1[-1] == '0' and b2[-1] == '0'
            return add_ bitwise(rest1, rest2) + '0'
        elif b1[-1] == '1' and b2[-1] == '1'
            return add_ bitwise(rest1, rest2) + '1'
"""this is the problematic line^^^"""