If you look at the node.js version of that sample,
https://github.com/googleapis/nodejs-dialogflow-cx/blob/main/samples/list-page.js , it includes the location in the parent parameter.
const listPageRequest = {
parent: `projects/${projectId}/locations/${location}/agents/${agentId}/flows/${flowId}`,
languageCode: 'en',
};
const response = await pagesClient.listPages(listPageRequest);
It doesn't acknowledge location anywhere else that I've noticed. You might (should?) be able to run the request in Python with a similar parent parameter. Also, btw, agentId and flowId are GUIDs, not friendly names like 'myAgent' or 'balanceFlow'.
-Ed