def list_variables(self, page_size=None, page_token=None, client=None):
        """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.
        """
        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
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.