[datetime.datetime] 当前快照数据的时间戳

def datetime(self):
        """
        [datetime.datetime] 当前快照数据的时间戳
        """
        try:
            dt = self._tick_dict['datetime']
        except (KeyError, ValueError):
            return datetime.datetime.min
        else:
            if not isinstance(dt, datetime.datetime):
                if dt > 10000000000000000:  # ms
                    return convert_ms_int_to_datetime(dt)
                else:
                    return convert_int_to_datetime(dt)
            return dt