code: def _create_flow(self, request_handler):
          
          if self.flow is None:
              redirect_uri = request_handler.request.relative_url(
                  self._callback_path)  # Usually /oauth2callback
              self.flow = client.OAuth2WebServerFlow(
                  self._client_id, self._client_secret, self._scope,
                  redirect_uri=redirect_uri, user_agent=self._user_agent,
                  auth_uri=self._auth_uri, token_uri=self._token_uri,
                  revoke_uri=self._revoke_uri, **self._kwargs)
docs: Create the Flow object.
  
          The Flow is calculated lazily since we don't know where this app is
          running until it receives a request, at which point redirect_uri can be
          calculated and then the Flow object can be constructed.
  
          Args:
              request_handler: webapp.RequestHandler, the request handler.