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:Version: 5.3.0b3
:Web: https://kombu.readthedocs.io/
:Download: https://pypi.org/project/kombu/
:Source: https://github.com/celery/kombu/
:Keywords: messaging, amqp, rabbitmq, redis, mongodb, python, queue
About
=====
`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`_, `redis`_, or `SQS`_ libraries.
* Virtual transports makes it really easy to add support for non-AMQP
transports. There is already built-in support for `Redis`_,
`Amazon SQS`_, `Azure Storage Queues`_, `Azure Service Bus`_,
`ZooKeeper`_, `SoftLayer MQ`_, `MongoDB`_ and `Pyro`_.
* 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`_.
.. _`RabbitMQ`: https://www.rabbitmq.com/
.. _`AMQP`: https://amqp.org
.. _`py-amqp`: https://pypi.org/project/amqp/
.. _`qpid-python`: https://pypi.org/project/qpid-python/
.. _`Redis`: https://redis.io/
.. _`Amazon SQS`: https://aws.amazon.com/sqs/
.. _`Azure Storage Queues`: https://azure.microsoft.com/en-us/services/storage/queues/
.. _`Azure Service Bus`: https://azure.microsoft.com/en-us/services/service-bus/
.. _`Zookeeper`: https://zookeeper.apache.org/
.. _`Rabbits and warrens`: http://web.archive.org/web/20160323134044/http://blogs.digitar.com/jjww/2009/01/rabbits-and-warrens/
.. _`amqplib`: http://barryp.org/software/py-amqplib/
.. _`Wikipedia article about AMQP`: http://en.wikipedia.org/wiki/AMQP
.. _`carrot`: https://pypi.org/project/carrot/
.. _`librabbitmq`: https://pypi.org/project/librabbitmq/
.. _`Pyro`: https://pyro4.readthedocs.io/
.. _`SoftLayer MQ`: http://www.softlayer.com/services/additional/message-queue
.. _`MongoDB`: https://www.mongodb.com/
.. _transport-comparison:
Transport Comparison
====================
+---------------+----------+------------+------------+---------------+--------------+-----------------------+
| **Client** | **Type** | **Direct** | **Topic** | **Fanout** | **Priority** | **TTL** |
+---------------+----------+------------+------------+---------------+--------------+-----------------------+
| *amqp* | Native | Yes | Yes | Yes | Yes [#f3]_ | Yes [#f4]_ |
+---------------+----------+------------+------------+---------------+--------------+-----------------------+
| *qpid* | Native | Yes | Yes | Yes | No | No |
+---------------+----------+------------+------------+---------------+--------------+-----------------------+
| *redis* | Virtual | Yes | Yes | Yes (PUB/SUB) | Yes | No |
+---------------+----------+------------+------------+---------------+--------------+-----------------------+
| *mongodb* | Virtual | Yes | Yes | Yes | Yes | Yes |
+---------------+----------+------------+------------+---------------+--------------+-----------------------+
| *SQS* | Virtual | Yes | Yes [#f1]_ | Yes [#f2]_ | No | No |
+---------------+----------+------------+------------+---------------+--------------+-----------------------+
| *zookeeper* | Virtual | Yes | Yes [#f1]_ | No | Yes | No |
+---------------+----------+------------+------------+---------------+--------------+-----------------------+
| *in-memory* | Virtual | Yes | Yes [#f1]_ | No | No | No |
+---------------+----------+------------+------------+---------------+--------------+-----------------------+
| *SLMQ* | Virtual | Yes | Yes [#f1]_ | No | No | No |
+---------------+----------+------------+------------+---------------+--------------+-----------------------+
| *Pyro* | Virtual | Yes | Yes [#f1]_ | No | No | No |
+---------------+----------+------------+------------+---------------+--------------+-----------------------+
.. [#f1] Declarations only kept in memory, so exchanges/queues
must be declared by all clients that needs them.
.. [#f2] Fanout supported via storing routing tables in SimpleDB.
Disabled by default, but can be enabled by using the
``supports_fanout`` transport option.
.. [#f3] AMQP Message priority support depends on broker implementation.
.. [#f4] AMQP Message/Queue TTL support depends on broker implementation.
Documentation
-------------
Kombu is using Sphinx, and the latest documentation can be found here:
https://kombu.readthedocs.io/
Quick overview
--------------
.. code-block:: python
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:
.. code-block:: python
with connection.channel() as channel:
producer = Producer(channel, ...)
consumer = Consumer(channel)
All objects can be used outside of with statements too,
just remember to close the objects after use:
.. code-block:: python
from kombu import Connection, Consumer
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.
.. code-block:: pycon
>>> 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.
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
A consumer declares a queue, binds it to an 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"`.
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