code: def xml(self, url, method='get', params=None, data=None):
          
          r = self.req(url, method, params, data)
          # this is required for avoid utf8-mb4 lead to encoding error
          return self.to_xml(r.content, base_url=r.url)
docs: 请求并返回xml
          
          :type url: str
          :param url: API
          
          :type method: str
          :param method: HTTP METHOD
          
          :type params: dict
          :param params: query
          
          :type data: dict
          :param data: body
          
          :rtype: html.HtmlElement
          :return: