code: def flush(self):
          
          if 'dbcl2' not in self.cookies:
              return
          r = self.req(API_ACCOUNT_HOME)
          if RE_SESSION_EXPIRE.search(r.url):
              return self.expire()
          self.cookies.update(dict(r.cookies))
          self.user_alias = slash_right(r.url)
          self.logger.debug('flush with user_alias <%s>' % self.user_alias)
          return
docs: 更新会话信息，主要是ck, user_alias