Book Image

Python Web Scraping - Second Edition

By : Katharine Jarmul
Book Image

Python Web Scraping - Second Edition

By: Katharine Jarmul

Overview of this book

The Internet contains the most useful set of data ever assembled, most of which is publicly accessible for free. However, this data is not easily usable. It is embedded within the structure and style of websites and needs to be carefully extracted. Web scraping is becoming increasingly useful as a means to gather and make sense of the wealth of information available online. This book is the ultimate guide to using the latest features of Python 3.x to scrape data from websites. In the early chapters, you'll see how to extract data from static web pages. You'll learn to use caching with databases and files to save time and manage the load on servers. After covering the basics, you'll get hands-on practice building a more sophisticated crawler using browsers, crawlers, and concurrent scrapers. You'll determine when and how to scrape data from a JavaScript-dependent website using PyQt and Selenium. You'll get a better understanding of how to submit forms on complex websites protected by CAPTCHA. You'll find out how to automate these actions with Python packages such as mechanize. You'll also learn how to create class-based scrapers with Scrapy libraries and implement your learning on real websites. By the end of the book, you will have explored testing websites with scrapers, remote scraping, best practices, working with images, and many other relevant topics.
Table of Contents (10 chapters)

When to use caching?

To cache, or not to cache? This is a question many programmers, data scientists, and web scrapers need to answer. In this chapter, we will show you how to use caching for your web crawlers; but should you use caching?

If you need to perform a large crawl, which may be interrupted due to an error or exception, caching can help by not forcing you to recrawl all the pages you might have already covered. Caching can also help you by allowing you to access those pages while offline (for your own data analysis or development purposes).

However, if having the most up-to-date and current information from the site is your highest priority, then caching might not make sense. In addition, if you don't plan large or repeated crawls, you might just want to scrape the page each time.

You may want to outline how often the pages you are scraping change or how often you should scrape new pages and clear...