https://firebase.google.com/docs/firestore/query-data/listen?hl=ja#python

firestore.listen.py

import threading
# pip install google-cloud-firestore
from google.cloud import firestore

import os
os.environ['GOOGLE_APPLICATION_CREDENTIALS'] = './push14-firebase-adminsdk-vgfzy-e8d93f3c32.json'
db = firestore.Client()
# Create an Event for notifying main thread.
callback_done = threading.Event()

first = False
import time
# Create a callback on_snapshot function to capture changes
def on_snapshot(doc_snapshot, changes, read_time):
    for doc in doc_snapshot:
        print(f'Received document snapshot: {doc.id}', changes, read_time, time.time())
    global first
    if first:
        callback_done.set()
    first = True

doc_ref = db.collection(u'cities').document(u'SF')
# latency: 55ms
# db.collection('cities').doc('SF').set({abc: Date.now()})
# Watch the document
doc_watch = doc_ref.on_snapshot(on_snapshot)

# Wait for the callback.
callback_done.wait()
# [START firestore_listen_detach]
# Terminate watch on a document
doc_watch.unsubscribe()