code: def start(self):
          '''Begin fetching the next request.'''
          self._current_session = session = self._http_client.session()
  
          request = self.next_request()
          assert request
  
          if request.url_info.password or \
                  request.url_info.hostname_with_port in self._hostnames_with_auth:
              self._add_basic_auth_header(request)
  
          response = yield from session.start(request)
  
          self._process_response(response)
  
          return responsf start(self):
          '''Begin fetching the next request.'''
          self._current_session = session = self._http_client.session()
  
          request = self.next_request()
          assert request
  
          if request.url_info.password or \
                  request.url_info.hostname_with_port in self._hostnames_with_auth:
              self._add_basic_auth_header(request)
  
          response = yield from session.start(request)
  
          self._process_response(response)
  
          return response
docs: Begin fetching the next request.