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_

.. |GA| image:: https://img.shields.io/badge/support-GA-gold.svg :target: https://github.com/googleapis/google-cloud-python/blob/main/README.rst#general-availability .. |pypi| image:: https://img.shields.io/pypi/v/google-cloud-pubsub.svg :target: https://pypi.org/project/google-cloud-pubsub/ .. |versions| image:: https://img.shields.io/pypi/pyversions/google-cloud-pubsub.svg :target: https://pypi.org/project/google-cloud-pubsub/ .. _Google Cloud Pub / Sub: https://cloud.google.com/pubsub/ .. _Product Documentation: https://cloud.google.com/pubsub/docs .. _Client Library Documentation: https://cloud.google.com/python/docs/reference/pubsub/latest

Quick Start

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

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

.. _Select or create a Cloud Platform project.: https://console.cloud.google.com/project .. _Enable billing for your project.: https://cloud.google.com/billing/docs/how-to/modify-project#enable_billing_for_a_project .. _Enable the Google Cloud Pub / Sub API.: https://cloud.google.com/pubsub .. _Setup Authentication.: https://googleapis.dev/python/google-api-core/latest/auth.html

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.

.. _`virtualenv`: https://virtualenv.pypa.io/en/latest/

Supported Python Versions
^^^^^^^^^^^^^^^^^^^^^^^^^
Python >= 3.7

Deprecated Python Versions
^^^^^^^^^^^^^^^^^^^^^^^^^^
Python <= 3.6.

The last version of this library compatible with Python 2.7 is google-cloud-pubsub==1.7.0.

Mac/Linux
^^^^^^^^^

.. code-block:: console

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

Windows
^^^^^^^

.. code-block:: console

    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

.. code-block:: python

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(name=topic_name)
future = publisher.publish(topic_name, b'My first message!', spam='eggs')
future.result()

To learn more, consult the publishing documentation_.

.. _publishing documentation: https://cloud.google.com/python/docs/reference/pubsub/latest

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.

.. code-block:: python

import os
from google.cloud import pubsub_v1

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.
)

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

with pubsub_v1.SubscriberClient() as subscriber:
    subscriber.create_subscription(
        name=subscription_name, topic=topic_name)  
    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:

.. code-block:: python

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_.

.. _subscriber documentation: https://cloud.google.com/python/docs/reference/pubsub/latest

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:

.. code-block:: python

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)

.. _Credentials: https://google-auth.readthedocs.io/en/latest/reference/google.auth.credentials.html#google.auth.credentials.Credentials .. _google-auth: https://google-auth.readthedocs.io/en/latest/index.html .. _google.auth.jwt.Credentials: https://google-auth.readthedocs.io/en/latest/reference/google.auth.jwt.html#google.auth.jwt.Credentials