def robotsrulesetOfDomain(self, domain):
		'''检查domain是否在数据库中,
			否 --> (False, None)
			是 --> (True, 数据库中存储的robots.txt内容)
		'''
		exist = False
		cur = self.conn.cursor()
		# 是否存在
		cur.execute("SELECT 1 FROM Domains WHERE domain=?", (domain,))
		if cur.fetchone() :
			exist = True
		# 存在的话,结果是什么
		cur.execute("SELECT rules FROM Domains,Rulesets "
			"WHERE domain=? AND Domains.did=Rulesets.did"
			,(domain,) )
		ruleset = cur.fetchone()
		return (exist, ruleset)
def log_exception(cls, msg):
        """Try to log an error message to this process's error log and the shared error log.

        NB: Doesn't raise (logs an error instead).
        """
        pid = os.getpid()
        fatal_error_log_entry = cls._format_exception_message(msg, pid)

        # We care more about this log than the shared log, so write to it first.
        try:
            cls._try_write_with_flush(cls._pid_specific_error_fileobj, fatal_error_log_entry)
        except Exception as e:
            logger.error(
                "Error logging the message '{}' to the pid-specific file handle for {} at pid {}:\n{}".format(
                    msg, cls._log_dir, pid, e
                )
            )

        # Write to the shared log.
        try:
            # TODO: we should probably guard this against concurrent modification by other pants
            # subprocesses somehow.
            cls._try_write_with_flush(cls._shared_error_fileobj, fatal_error_log_entry)
        except Exception as e:
            logger.error(
                "Error logging the message '{}' to the shared file handle for {} at pid {}:\n{}".format(
                    msg, cls._log_dir, pid, e
                )
            )