code: def list_variables(self, page_size=None, page_token=None, client=None):
          
          path = "%s/variables" % (self.path,)
          client = self._require_client(client)
          iterator = page_iterator.HTTPIterator(
              client=client,
              api_request=client._connection.api_request,
              path=path,
              item_to_value=_item_to_variable,
              items_key="variables",
              page_token=page_token,
              max_results=page_size,
          )
          iterator._MAX_RESULTS = "pageSize"
          iterator.config = self
          return iterator
docs: API call:  list variables for this config.
  
          This only lists variable names, not the values.
  
          See
          https://cloud.google.com/deployment-manager/runtime-configurator/reference/rest/v1beta1/projects.configs.variables/list
  
          :type page_size: int
          :param page_size:
              Optional. The maximum number of variables in each page of results
              from this request. Non-positive values are ignored. Defaults
              to a sensible value set by the API.
  
          :type page_token: str
          :param page_token:
              Optional. If present, return the next batch of variables, using
              the value, which must correspond to the ``nextPageToken`` value
              returned in the previous response.  Deprecated: use the ``pages``
              property of the returned iterator instead of manually passing
              the token.
  
          :type client: :class:`~google.cloud.runtimeconfig.client.Client`
          :param client:
              (Optional) The client to use.  If not passed, falls back to the
              ``client`` stored on the current config.
  
          :rtype: :class:`~google.api_core.page_iterator.Iterator`
          :returns:
              Iterator of :class:`~google.cloud.runtimeconfig.variable.Variable`
              belonging to this project.