We will implement two simple but interesting applications using Celery. The first one is a reimplementation of the currency exchange rate example from Chapter 3, Parallelism in Python, and the second one is a distributed sort algorithm.

We are going to use a total of four machines again (HOST1, HOST2, HOST3, and HOST4) for all these examples. As we did before, machine one (HOST1) will run RabbitMQ. The second machine (HOST2) will run Redis, the third one (HOST3) will run Celery workers, and finally, the fourth one (HOST4) will run our main code.

Let's start with a simple example. Create a new Python script (celery/currency.py) and write the following code (if you're not using Redis, remember to change backend to 'amqp://HOST1'):

import celery
import urllib.request


app = celery.Celery('currency',
                    broker='amqp://HOST1',
                    backend='redis://HOST2')


URL = 'http://finance.yahoo.com/d/quotes.csv?s={}=X&f=p'

@app.task...