Hi Agung. Yes, the Python runtime of Google Cloud Functions uses Flask to dispatch incoming requests. Here’s the confirmation from the documentation: https://cloud.google.com/functions/docs/concepts/python-runtime#http_library
Please note that at the moment there’s no “Cloud Functions for Firebase” offering in Python. That’s only available in Node.js right now. This means Python developers are currently limited to the standard function triggers provided by Google Cloud Functions, which includes HTTP triggers, Storage triggers and perhaps a couple of others. Firebase triggers (Firestore, auth, RTDB etc) are not yet available in Python.