code: def fetch_post_data(self):
          '''
          fetch post accessed data. post_data, and ext_dic.
          '''
          post_data = {}
          ext_dic = {}
          for key in self.request.arguments:
              if key.startswith('def_'):
                  ext_dic[key] = self.get_argument(key)
              else:
                  post_data[key] = self.get_arguments(key)[0]
  
          post_data['user_name'] = self.userinfo.user_name
  
          ext_dic = dict(ext_dic, **self.ext_post_data(postdata=post_data))
  
          return (post_data, ext_dicf fetch_post_data(self):
          '''
          fetch post accessed data. post_data, and ext_dic.
          '''
          post_data = {}
          ext_dic = {}
          for key in self.request.arguments:
              if key.startswith('def_'):
                  ext_dic[key] = self.get_argument(key)
              else:
                  post_data[key] = self.get_arguments(key)[0]
  
          post_data['user_name'] = self.userinfo.user_name
  
          ext_dic = dict(ext_dic, **self.ext_post_data(postdata=post_data))
  
          return (post_data, ext_dic)
docs: fetch post accessed data. post_data, and ext_dic.