Python Client for Google Cloud Pub / Sub

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.

• Product Documentation

• Client Library Documentation

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) publish 
er. 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 = subscribe 
r. 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)