code: def to_str(s):
      
      if bytes != str:
          """
          这里的比较在python2中是True，在Python3中是False
          """
          if type(s) == bytes:
              return s.decode('utf-8')
      return s
docs: 将字节数组转成成字符串
      :param s: 字节数组
      :return: 字符串