Implementation

Let's implement a program to fetch content from web pages, inspired by the tutorial from Michael Ford (https://docs.python.org/3/howto/urllib2.html). We have only take the simple part since the focus is to illustrate our pattern more than it is to build a special web-scraping tool.

We will use the urllib module to connect to web pages using their URLs; the core of the program would be the URLFetcher class that takes care of doing the work via a fetch() method.

We want to be able to track the list of web pages that were tracked, hence the use of the singleton pattern: we need a single object to maintain that global state.

First, our naive version, inspired by the tutorial but modified to help us track the list of URLs that ...

Get Mastering Python Design Patterns - Second Edition now with O’Reilly online learning.

O’Reilly members experience live online training, plus books, videos, and digital content from 200+ publishers.