两数相加

if not x:

    return 0

str_x = str(x)

start = ''

if str_x[0] == '-':

    start = '-'

    temp = start + str_x[::-1].lstrip('0').rstrip('-')

    output = int(temp)

 if -2**31 <= output <= 2**31-1:         

        return output

  else:

        return 0