Messaging library for Python
Project description
- Version:
- 3.0.3
Kombu is a messaging library for Python.
The aim of Kombu is to make messaging in Python as easy as possible by providing an idiomatic high-level interface for the AMQ protocol, and also provide proven and tested solutions to common messaging problems.
AMQP is the Advanced Message Queuing Protocol, an open standard protocol for message orientation, queuing, routing, reliability and security, for which the RabbitMQ messaging server is the most popular implementation.
Features
Allows application authors to support several message server solutions by using pluggable transports.
AMQP transport using the py-amqp or librabbitmq client libraries.
High performance AMQP transport written in C - when using librabbitmq
This is automatically enabled if librabbitmq is installed:
$ pip install librabbitmq
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, MongoDB, ZeroMQ, ZooKeeper, SoftLayer MQ and Pyro.
You can also use the SQLAlchemy and Django ORM transports to use a database as the broker.
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 |
amqp |
Native |
Yes |
Yes |
Yes |
redis |
Virtual |
Yes |
Yes |
Yes (PUB/SUB) |
mongodb |
Virtual |
Yes |
Yes |
Yes |
beanstalk |
Virtual |
Yes |
Yes [1] |
No |
SQS |
Virtual |
Yes |
Yes [1] |
Yes [2] |
couchdb |
Virtual |
Yes |
Yes [1] |
No |
zookeeper |
Virtual |
Yes |
Yes [1] |
No |
in-memory |
Virtual |
Yes |
Yes [1] |
No |
django |
Virtual |
Yes |
Yes [1] |
No |
sqlalchemy |
Virtual |
Yes |
Yes [1] |
No |
SLMQ |
Virtual |
Yes |
Yes [1] |
No |
Documentation
Kombu is using Sphinx, and the latest documentation can be found here:
Quick overview
from kombu import Connection, 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 Connection('amqp://guest:guest@localhost//') as conn:
# produce
producer = conn.Producer(serializer='json')
producer.publish({'name': '/tmp/lolcat1.avi', 'size': 1301013},
exchange=media_exchange, routing_key='video',
declare=[video_queue])
# the declare above, makes sure the video queue is declared
# so that the messages can be delivered.
# It's a best practice in Kombu to have both publishers and
# consumers declare the queue. You can also declare the
# queue manually using:
# video_queue(conn).declare()
# 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 Connection, Consumer, Producer
connection = Connection()
# ...
connection.release()
consumer = Consumer(channel_or_connection, ...)
consumer.register_callback(my_callback)
consumer.consume()
# ....
consumer.cancel()
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.
Binding exchanges and queues to a connection will make it use that connections default channel.
>>> exchange = Exchange('tasks', 'direct')
>>> connection = Connection()
>>> bound_exchange = exchange(connection)
>>> 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/celery/kombu/issues/
Contributing
Development of Kombu happens at Github: http://github.com/celery/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.
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