OBSOLETE, see comment below ||| Connection to the Firestore emulator in python, since it wasn't at that time supported by the official SDK, see https://github.com/googleapis/google-cloud-python/issues/7500

firestore_emulator.py

import os
from unittest import mock

import grpc
from google.auth.credentials import Credentials
from google.cloud import firestore
from google.cloud.firestore_v1.gapic import firestore_client
from google.cloud.firestore_v1.gapic.transports import firestore_grpc_transport


def get_firestore_client() -> firestore.Client:
    """
    Return a firestore Client, connects to an emulator if FIREBASE_FIRESTORE_EMULATOR_ADDRESS is set

    eg, using https://firebase.google.com/docs/functions/local-emulator

    firebase emulators:start --only firestore
    :return:
    """

    emulator_address = os.environ.get("FIREBASE_FIRESTORE_EMULATOR_ADDRESS")

    if emulator_address:
        dummy_project = "foo"
        dummy_credentials = mock.MagicMock(spec=Credentials)

        db = firestore.Client(project=dummy_project, credentials=dummy_credentials)

        # hack - set the internal firestore api client to point at the emulator,
        # used by ref: google.cloud.firestore_v1.client.Client._firestore_api
        print(f"connecting to firestore emulator at {emulator_address}")
        channel = grpc.insecure_channel(emulator_address)
        transport = firestore_grpc_transport.FirestoreGrpcTransport(channel=channel)
        db._firestore_api_internal = firestore_client.FirestoreClient(transport=transport)
    else:
        db = firestore.Client()

    return db

Note: firestore_client.FirestoreClient is not process safe, since it can't be pickled.
Maybe we can hack up a Mutex wrapper...

Also worth noting that this configuration is only good for testing rules for an unauthenticated user - I'm trying to figure out how to feed in a JWT that authenticates a given user so it can be used to test rules that use request.auth.uid.

In the Node SDK this can be done as follows:

 firebase.initializeTestApp({
   projectId: "my-test-project",
   auth: { uid: "alice", email: "alice@example.com" }
 });

https://firebase.google.com/docs/firestore/security/test-rules-emulator#run_local_tests

I think this is now obsolete, since https://github.com/googleapis/google-cloud-python/pull/8721/files it's now possible to connect to the firestore emulator as admin by just setting the following environment variables:

export FIRESTORE_EMULATOR_HOST=localhost:8080
# needs to be set otherwise so the client can determine project id, but it can be any string in google cloud project id format.
export GOOGLE_CLOUD_PROJECT=any-thing

Thank you @therefromhere! This is very useful for me 🙂

I'm waiting for the Firebase Authentication <-> python admin sdk integration. For those who are interested:
firebase/firebase-admin-python#531