def insertDomain(self, domain, indegree=0, outdegree=0):
		'''增加一个域名'''
		cur = self.conn.cursor()
		cur.execute("INSERT INTO Domains VALUES (NULL,?,?,?)", (domain, indegree, outdegree))
		# 写入到文件中
		self.conn.commit()
def _safe_close(self, sess):
    """Closes a session without raising an exception.

    Just like sess.close() but ignores exceptions.

    Args:
      sess: A `Session`.
    """
    # pylint: disable=broad-except
    try:
      sess.close()
    except Exception:
      # Intentionally not logging to avoid user complaints that
      # they get cryptic errors.  We really do not care that Close
      # fails.
      pass
    # pylint: enable=broad-except