kombu - Messaging Framework for Python

Version:2.1.8

Synopsis

Kombu is an AMQP messaging framework for Python.

AMQP is the Advanced Message Queuing Protocol, an open standard protocol for message orientation, queuing, routing, reliability and security.

One of the most popular implementations of AMQP is RabbitMQ.

The aim of Kombu is to make messaging in Python as easy as possible by providing an idiomatic high-level interface for the AMQP protocol, and also provide proven and tested solutions to common messaging problems.

Features

• Allows application authors to support several message server solutions by using pluggable transports.

  • AMQP transports for both the amqplib (sync) and pika (sync + async) clients.
  • Virtual transports makes it really easy to add support for non-AMQP transports. There is already built-in support for Redis, Beanstalk, Amazon SQS, CouchDB, and MongoDB.
  • SQLAlchemy and Django ORM transports exists as plug-ins ( kombu-sqlalchemy and django-kombu).
  • In-memory transport for unit testing.

• Supports automatic encoding, serialization and compression of message payloads.

• Consistent exception handling across transports.

• The ability to ensure that an operation is performed by gracefully handling connection and channel errors.

• Several annoyances with amqplib has been fixed, like supporting timeouts and the ability to wait for events on more than one channel.

• Projects already using carrot can easily be ported by using a compatibility layer.

For an introduction to AMQP you should read the article Rabbits and warrens, and the Wikipedia article about AMQP.

Transport Comparison

Client	Type	Direct	Topic	Fanout
amqplib	Native	Yes	Yes	Yes
pika	Native	Yes	Yes	Yes
redis	Virtual	Yes	Yes [1]	Yes (PUB/SUB)
beanstalk	Virtual	Yes	Yes [1]	No
SQS	Virtual	Yes	Yes [1]	Yes [2]
mongodb	Virtual	Yes	Yes [1]	Yes
couchdb	Virtual	Yes	Yes [1]	No
in-memory	Virtual	Yes	Yes [1]	No

[1]	(1, 2, 3, 4, 5, 6) Declarations only kept in memory, so exchanges/queues must be declared by all clients that needs them.

[2]	Fanout supported via storing routing tables in SimpleDB. Disabled by default, but can be enabled by using the supports_fanout transport option.

Documentation

Kombu is using Sphinx, and the latest documentation is available at GitHub:

http://ask.github.com/kombu

Quick overview

from kombu import BrokerConnection, Exchange, Queue

media_exchange = Exchange("media", "direct", durable=True)
video_queue = Queue("video", exchange=media_exchange, routing_key="video")

def process_media(body, message):
    print body
    message.ack()

# connections
with BrokerConnection("amqp://guest:guest@localhost//") as conn:

    # Declare the video queue so that the messages can be delivered.
    # It is a best practice in Kombu to have both publishers and
    # consumers declare the queue.
    video_queue(conn.channel()).declare()

    # produce
    with conn.Producer(exchange=media_exchange,
                       serializer="json", routing_key="video") as producer:
        producer.publish({"name": "/tmp/lolcat1.avi", "size": 1301013})

    # consume
    with conn.Consumer(video_queue, callbacks=[process_media]) as consumer:
        # Process messages and handle events on all channels
        while True:
            conn.drain_events()

# Consume from several queues on the same channel:
video_queue = Queue("video", exchange=media_exchange, key="video")
image_queue = Queue("image", exchange=media_exchange, key="image")

with connection.Consumer([video_queue, image_queue],
                         callbacks=[process_media]) as consumer:
    while True:
        connection.drain_events()

Or handle channels manually:

with connection.channel() as channel:
    producer = Producer(channel, ...)
    consumer = Producer(channel)

All objects can be used outside of with statements too, just remember to close the objects after use:

from kombu import BrokerConnection, Consumer, Producer

connection = BrokerConnection()
    # ...
connection.close()

consumer = Consumer(channel_or_connection, ...)
consumer.register_callback(my_callback)
consumer.consume()
    # ....
consumer.cancel()


producer = Producer(channel_or_connection, ...)
    # ....
producer.close()

Exchange and Queue are simply declarations that can be pickled and used in configuration files etc.

They also support operations, but to do so they need to be bound to a channel:

>>> exchange = Exchange("tasks", "direct")

>>> connection = BrokerConnection()
>>> channel = connection.channel()
>>> bound_exchange = exchange(channel)
>>> bound_exchange.delete()

# the original exchange is not affected, and stays unbound.
>>> exchange.delete()
raise NotBoundError: Can't call delete on Exchange not bound to
    a channel.

Installation

You can install Kombu either via the Python Package Index (PyPI) or from source.

To install using pip,:

$ pip install kombu

To install using easy_install,:

$ easy_install kombu

If you have downloaded a source tarball you can install it by doing the following,:

$ python setup.py build
# python setup.py install # as root

Terminology

There are some concepts you should be familiar with before starting:

• Producers

  Producers sends messages to an exchange.

• Exchanges

  Messages are sent to exchanges. Exchanges are named and can be configured to use one of several routing algorithms. The exchange routes the messages to consumers by matching the routing key in the message with the routing key the consumer provides when binding to the exchange.

• Consumers

  Consumers declares a queue, binds it to a exchange and receives messages from it.

• Queues

  Queues receive messages sent to exchanges. The queues are declared by consumers.

• Routing keys

  Every message has a routing key. The interpretation of the routing key depends on the exchange type. There are four default exchange types defined by the AMQP standard, and vendors can define custom types (so see your vendors manual for details).

  These are the default exchange types defined by AMQP/0.8:

  • Direct exchange

    Matches if the routing key property of the message and the routing_key attribute of the consumer are identical.

  • Fan-out exchange

    Always matches, even if the binding does not have a routing key.

  • Topic exchange

    Matches the routing key property of the message by a primitive pattern matching scheme. The message routing key then consists of words separated by dots (”.”, like domain names), and two special characters are available; star (“*”) and hash (“#”). The star matches any word, and the hash matches zero or more words. For example “*.stock.#” matches the routing keys “usd.stock” and “eur.stock.db” but not “stock.nasdaq”.

Getting Help

Mailing list

Join the carrot-users mailing list.

Bug tracker

If you have any suggestions, bug reports or annoyances please report them to our issue tracker at http://github.com/ask/kombu/issues/

Contributing

Development of Kombu happens at Github: http://github.com/ask/kombu

You are highly encouraged to participate in the development. If you don’t like Github (for some reason) you’re welcome to send regular patches.

License

This software is licensed under the New BSD License. See the LICENSE file in the top distribution directory for the full license text.