def shutdown_kernel(self):
        """Shutdown the kernel of the client."""
        kernel_id = self.get_kernel_id()

        if kernel_id:
            delete_url = self.add_token(url_path_join(self.server_url,
                                                      'api/kernels/',
                                                      kernel_id))
            delete_req = requests.delete(delete_url)
            if delete_req.status_code != 204:
                QMessageBox.warning(
                    self,
                    _("Server error"),
                    _("The Jupyter Notebook server "
                      "failed to shutdown the kernel "
                      "associated with this notebook. "
                      "If you want to shut it down, "
                      "you'll have to close Spyder."))
Shutdown the kernel of the client.