A lightweight and simpler alternative to Celery is Python-RQ (http://python-rq.org). It is based on Redis alone as a provider of both task queue and result backend. It is intended for those applications where complex task dependencies or task routing is not necessary.

Since Celery and Python-RQ are conceptually very similar, let's jump right in and rewrite one of our earlier examples. Create a new Python script (rq/currency.py) with the following command:

import urllib.request


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


def get_rate(pair, url_tmplt=URL):
    # raise Exception('Booo!')

    with urllib.request.urlopen(url_tmplt.format(pair)) as res:
        body = res.read()
    return (pair, float(body.strip()))

This is simply the same code from all the currency examples that we saw so far—nothing new here. The main difference with the Celery implementation is that this code has no dependency on Python-RQ or Redis. Copy this script to the...