code: def strftime(date_time=None, time_format=None):
          
          if not date_time:
              datetime_now = datetime.now()
          else:
              datetime_now = date_time
          if not time_format:
              time_format = '%Y/%m/%d %H:%M:%S'
          return datetime.strftime(datetime_now, time_format)
docs: 将 datetime 对象转换为 str
  
          :param:
              * date_time: (obj) datetime 对象
              * time_format: (sting) 日期格式字符串
          :return:
              * date_time_str: (string) 日期字符串