def set_expire(self, new_expire, only_read=False):
        """
        >>> cache = Cache(log_level=logging.WARNING)
        >>> cache.set_expire(40)
        >>> cache.expire
        40
        >>> cache.set_expire('haha')
        >>> cache.expire
        40
        """
        if not isinstance(new_expire, int) or new_expire < 0:
            self.logger.warning('Parameter new_expire %s must be positive number' % new_expire)
            return
        self.expire = new_expire
>>> cache = Cache(log_level=logging.WARNING)
        >>> cache.set_expire(40)
        >>> cache.expire
        40
        >>> cache.set_expire('haha')
        >>> cache.expire
        40