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Python tutorial
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‎python/receive.py‎

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#!/usr/bin/env python
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import pika
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connection = pika.AsyncoreConnection(pika.ConnectionParameters(
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host='127.0.0.1',
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credentials=pika.PlainCredentials('guest', 'guest')))
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channel = connection.channel()
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channel.queue_declare(queue='test')
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def callback(ch, method, header, body):
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print " [x] Received %.20r" % (body,)
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channel.basic_consume(callback,
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queue='test',
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no_ack=True)
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print ' [*] Waiting for messages. To exit press CTRL+C'
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pika.asyncore_loop()

‎python/send.py‎

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#!/usr/bin/env python
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import pika
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connection = pika.AsyncoreConnection(pika.ConnectionParameters(
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host='127.0.0.1',
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credentials=pika.PlainCredentials('guest', 'guest')))
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channel = connection.channel()
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channel.queue_declare(queue='test')
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channel.basic_publish(exchange='',
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routing_key='test',
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body='Hello World!')
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print " [x] Sent 'Hello World!'"
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‎python/tutorial-one.md‎

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<!---
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title: Learning RabbitMQ, part 1 (Hello world!)
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layout: post
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--->
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Learning RabbitMQ, part 1 ("Hello world!")
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==========================================
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<!--
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{% dot -Gsize="10,1.3" -Grankdir=LR %}
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digraph G {
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P1 [label="P", {{ site.dotstyle.producer }}];
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Q1 [label="{<s>||||<e>}", {{ site.dotstyle.queue }}];
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C1 [label="C", {{ site.dotstyle.consumer }}];
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P1 -> Q1 -> C1;
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}
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{% enddot %}
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-->
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Throughout this tutorial, we'll teach you the basic concepts required for
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creating RabbitMQ applications. The tutorial will be illustrated with
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code snippets written in [Python](http://www.python.org/). But don't worry if
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you don't know this language - the core ideas are the same for other languages.
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This tutorial consists of three parts:
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* First we're going to write the simplest possible "Hello World" example.
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* Next we'll try to use Rabbit as a simple "Work queue" server.
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* Finally, we'll discuss the "Publish-subscribe" pattern.
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You need to have RabbitMQ server installed to go throught this tutorial.
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If you haven't installed it yet you can follow the [installation instructions](http://www.rabbitmq.com/install.html). You can tell RabbitMQ is installed by checking if the tcp/ip port 5672 is opened. For example if you have installed RabbitMQ you should see something like:
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$ nc -vz localhost 5672
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localhost [127.0.0.1] 5672 (tcp/amqp) open
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<!--
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<div class="info" markdown="1">
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-->
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#### Where to get help
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If you’re having trouble going through this tutorial you can post a message to
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[rabbitmq-discuss mailing list](https://lists.rabbitmq.com/cgi-bin/mailman/listinfo/rabbitmq-discuss).
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<!--
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</div>
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-->
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Introduction
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------------
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RabbitMQ is a message broker. The principle idea is pretty simple: it accepts
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and forwards messages. You can think about it as a post office: when you send
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mail to the post box and you're pretty sure that mr postman will eventually
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deliver the mail to your recipient. Using this metaphor RabbitMQ is a post box,
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post office and a mailman.
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The major difference between RabbitMQ and the post office is the fact that it
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doesn't deal with the paper, instead it accepts, stores and forwards binary
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blobs of data - _messages_.
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RabbitMQ uses a weird jargon, but it's simple once you'll get it. For example:
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* _Producing_ means nothing more than sending. A program that sends messages
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is a _producer_.
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<!--
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{% dot -Gsize="10,0.3" -Grankdir=LR%}
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digraph G {
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P1 [label="P", {{ site.dotstyle.producer }}];
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}
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{% enddot %}
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-->
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* _A queue_ is the name for a mailbox. It lives inside RabbitMQ.
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{% dot -Gsize="10,0.3" -Grankdir=LR%}
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<!--
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digraph G {
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Q1 [label="{<s>||||<e>}", {{ site.dotstyle.queue }}];
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}
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{% enddot %}
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-->
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* _Consuming_ has a simmilar meaning to receiving. _Consumer_ is a program
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that mostly waits to receive messages.
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<!--
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{% dot -Gsize="10,0.3" -Grankdir=LR %}
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digraph G {
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C1 [label="C", {{ site.dotstyle.consumer }}];
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}
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{% enddot %}
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-->
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Hello World!
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------------
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Our first "Hello world" won't be too complex - let's send a message, receive
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it and print it on the screen. To do so we need two programs, well, one that
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sends a message and one that receives and prints it.
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<!--
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Our overall design will look like:
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{% dot -Gsize="10,0.8" -Grankdir=LR %}
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digraph G {
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P1 [label="P", {{ site.dotstyle.producer }}];
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Q1 [label="{<s>||||<e>}", {{ site.dotstyle.queue }}];
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C1 [label="C", {{ site.dotstyle.consumer }}];
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P1 -> Q1 -> C1;
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}
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{% enddot %}
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-->
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Creating a program
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------------------
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<!--
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<div class="info" markdown="1">
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-->
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#### RabbitMQ libraries
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RabbitMQ speaks AMQP protocol. To use Rabbit you'll need a library that
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understands the same protocol as Rabbit. There is a choice of libraries
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for almost every programming language. Python it's not different and there is
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a bunch of libraries to choose from:
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* [py-amqplib](http://barryp.org/software/py-amqplib/)
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* [txAMQP](https://launchpad.net/txamqp)
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* [pika](http://github.com/tonyg/pika)
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In this tutorial we're going to use `pika`. To install it you can use [`pip`](http://pip.openplans.org/) package management tool:
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$ sudo pip install -e git://github.com/tonyg/pika.git#egg=pika
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If you don't have `pip`, you may want to install it.
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* On Ubuntu:
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$ sudo apt-get install python-pip
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* On Debian:
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$ sudo apt-get install python-setuptools
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$ sudo easy_install pip
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<!--
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</div>
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-->
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### Sending
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<!--
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{% dot -Gsize="10,0.5" -Grankdir=LR %}
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digraph G {
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P1 [label="P", {{ site.dotstyle.producer }}];
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Q1 [label="{<s>||||<e>}", {{ site.dotstyle.queue }}];
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P1 -> Q1;
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}
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{% enddot %}
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-->
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Our first program `send.py` will send a single message to the queue.
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The first thing we need to do is to connect to RabbitMQ server.
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<!--
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{% highlight python linenos=true linenostart=1 %}
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-->
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#!/usr/bin/env python
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import pika
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connection = pika.AsyncoreConnection(pika.ConnectionParameters(
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'127.0.0.1',
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credentials = pika.PlainCredentials('guest', 'guest'))
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channel = connection.channel()
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<!--
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{% endhighlight %}
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-->
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Whenever we send a message we need to make sure the recipient queue exists.
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RabbitMQ will just trash the message if can't deliver it. So, we need to
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create a queue to which the message will be delivered. Let's name this queue
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_test_:
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<!--
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{% highlight python linenos=true linenostart=8 %}
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-->
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channel.queue_declare(queue='test')
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<!--
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{% endhighlight %}
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-->
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At that point we're ready to send a message. Our first message will contain
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a string _Hello World!_. We are going to send it to our _test_ queue:
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<!--
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{% highlight python linenos=true linenostart=9 %}
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-->
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channel.basic_publish(exchange='',
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routing_key='test',
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body='Hello World!')
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print " [x] Sent 'Hello World!'"
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<!--
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{% endhighlight %}
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-->
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[(full send.py source)](http://github.com/rabbitmq/rabbitmq-tutorials/blob/master/python/send.py)
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### Receiving
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<!--
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{% dot -Gsize="10,0.5" -Grankdir=LR %}
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digraph G {
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rankdir=LR;
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Q1 [label="{<s>||||<e>}", {{ site.dotstyle.queue }}];
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C1 [label="C", {{ site.dotstyle.consumer }}];
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Q1 -> C1;
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}
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{% enddot %}
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-->
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Our second program `receive.py` will receive messages from the queue and print
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them on the screen.
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The code responsible for connecting to Rabbit is the same as in previous example.
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You can copy the first 7 lines.
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# ... connection code is the same, copy first 7 lines from send.py ...
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Just like before, in the beginning we must make sure that the
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queue exists. Creating a queue using `queue_declare` is idempotent - you can
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run the command as many times you'd like, and only one queue will be created.
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<!--
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{% highlight python linenos=true linenostart=8 %}
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-->
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channel.queue_declare(queue='test')
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<!--
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{% endhighlight %}
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-->
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Receiving messages from the queue is a bit more complex. Whenever we receive
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a message, a `callback` function is called. In our case
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this function will print on the screen the contents of the message.
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<!--
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{% highlight python linenos=true linenostart=9 %}
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-->
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def callback(ch, method, header, body):
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print " [x] Received %.20r" % (body,)
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<!--
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{% endhighlight %}
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-->
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Next, we need to tell RabbitMQ that this particular callback function is
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interested in messages from our _test_ queue:
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<!--
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{% highlight python linenos=true linenostart=11 %}
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-->
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channel.basic_consume(callback,
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queue='test',
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no_ack=True)
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<!--
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{% endhighlight %}
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-->
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And finally, we enter never-ending loop that waits for data and runs callbacks
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whenever necessary.
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<!--
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{% highlight python linenos=true linenostart=14 %}
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-->
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print ' [*] Waiting for messages. To exit press CTRL+C'
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pika.asyncore_loop()
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<!--
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{% endhighlight %}
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-->
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[(full receive.py source)](http://github.com/rabbitmq/rabbitmq-tutorials/blob/master/python/receive.py)
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### Putting it all together
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Now we can try out our programs. First, let's send
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a message using our `send.py` program:
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$ python send.py
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[x] Sent 'Hello World!'
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Let's receive it:
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$ python receive.py
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[*] Waiting for messages. To exit press CTRL+C
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[x] Received 'Hello World!'
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Hurray! We were able to send our first message through RabbitMQ. As you might
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have noticed, the `receive.py` program haven't exited. It will stay ready to
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receive further messages. Try to run `send.py` in new terminal!

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