Python Client for Google Cloud Pub / Sub#

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Google Cloud Pub / Sub is a fully-managed real-time messaging service that allows you to send and receive messages between independent applications. You can leverage Cloud Pub/Sub’s flexibility to decouple systems and components hosted on Google Cloud Platform or elsewhere on the Internet. By building on the same technology Google uses, Cloud Pub / Sub is designed to provide “at least once” delivery at low latency with on-demand scalability to 1 million messages per second (and beyond).

Publisher applications can send messages to a topic and other applications can subscribe to that topic to receive the messages. By decoupling senders and receivers, Google Cloud Pub/Sub allows developers to communicate between independently written applications.

Quick Start#

In order to use this library, you first need to go through the following steps:

  1. Select or create a Cloud Platform project.
  2. Enable billing for your project.
  3. Enable the Google Cloud Pub / Sub API.
  4. Setup Authentication.

Installation#

Install this library in a virtualenv using pip. virtualenv is a tool to create isolated Python environments. The basic problem it addresses is one of dependencies and versions, and indirectly permissions.

With virtualenv, it’s possible to install this library without needing system install permissions, and without clashing with the installed system dependencies.

Supported Python Versions#

Python >= 3.5

Deprecated Python Versions#

Python == 2.7. Python 2.7 support will be removed on January 1, 2020.

Mac/Linux#

pip install virtualenv
virtualenv <your-env>
source <your-env>/bin/activate
<your-env>/bin/pip install google-cloud-pubsub

Windows#

pip install virtualenv
virtualenv <your-env>
<your-env>\Scripts\activate
<your-env>\Scripts\pip.exe install google-cloud-pubsub

Example Usage#

Publishing#

To publish data to Cloud Pub/Sub you must create a topic, and then publish messages to it

import os
from google.cloud import pubsub_v1

publisher = pubsub_v1.PublisherClient()
topic_name = 'projects/{project_id}/topics/{topic}'.format(
    project_id=os.getenv('GOOGLE_CLOUD_PROJECT'),
    topic='MY_TOPIC_NAME',  # Set this to something appropriate.
)
publisher.create_topic(topic_name)
publisher.publish(topic_name, b'My first message!', spam='eggs')

To learn more, consult the publishing documentation.

Subscribing#

To subscribe to data in Cloud Pub/Sub, you create a subscription based on the topic, and subscribe to that, passing a callback function.

import os
from google.cloud import pubsub_v1

subscriber = pubsub_v1.SubscriberClient()
topic_name = 'projects/{project_id}/topics/{topic}'.format(
    project_id=os.getenv('GOOGLE_CLOUD_PROJECT'),
    topic='MY_TOPIC_NAME',  # Set this to something appropriate.
)
subscription_name = 'projects/{project_id}/subscriptions/{sub}'.format(
    project_id=os.getenv('GOOGLE_CLOUD_PROJECT'),
    sub='MY_SUBSCRIPTION_NAME',  # Set this to something appropriate.
)
subscriber.create_subscription(
    name=subscription_name, topic=topic_name)

def callback(message):
    print(message.data)
    message.ack()

future = subscriber.subscribe(subscription_name, callback)

The future returned by the call to subscriber.subscribe can be used to block the current thread until a given condition obtains:

try:
    future.result()
except KeyboardInterrupt:
    future.cancel()

It is also possible to pull messages in a synchronous (blocking) fashion. To learn more about subscribing, consult the subscriber documentation.

Authentication#

It is possible to specify the authentication method to use with the Pub/Sub clients. This can be done by providing an explicit Credentials instance. Support for various authentication methods is available from the google-auth library.

For example, to use JSON Web Tokens, provide a google.auth.jwt.Credentials instance:

import json
from google.auth import jwt

service_account_info = json.load(open("service-account-info.json"))
audience = "https://pubsub.googleapis.com/google.pubsub.v1.Subscriber"

credentials = jwt.Credentials.from_service_account_info(
    service_account_info, audience=audience
)

subscriber = pubsub_v1.SubscriberClient(credentials=credentials)

# The same for the publisher, except that the "audience" claim needs to be adjusted
publisher_audience = "https://pubsub.googleapis.com/google.pubsub.v1.Publisher"
credentials_pub = credentials.with_claims(audience=publisher_audience)
publisher = pubsub_v1.PublisherClient(credentials=credentials_pub)