Preface

The internet contains the most useful set of data ever assembled, largely publicly accessible for free. However this data is not easily re-usable. It is embedded within the structure and style of websites and needs to be extracted to be useful. This process of extracting data from webpages is known as web scraping and is becoming increasingly useful as ever more information is available online.

All code used has been tested with Python 3.4+ and is available for download at https://github.com/kjam/wswp.

 

What this book covers

Chapter 1, Introduction to Web Scraping, introduces what is web scraping and how to crawl a website.

Chapter 2, Scraping the Data, shows you how to extract data from webpages using several libraries.

Chapter 3, Caching Downloads, teaches how to avoid re downloading by caching results.

Chapter 4, Concurrent Downloading, helps you how to scrape data faster by downloading websites in parallel.

Chapter 5, Dynamic Content, learn about how to extract data from dynamic websites through several means.

Chapter 6, Interacting with Forms, shows how to work with forms such as inputs and navigation for search and login.

Chapter 7, Solving CAPTCHA, elaborates how to access data protected by CAPTCHA images.

Chapter 8, Scrapy, learn how to use Scrapy crawling spiders for fast and parallelized scraping and the Portia web interface to build a web scraper.

Chapter 9, Putting It All Together, an overview of web scraping techniques you have learned via this book.

What you need for this book

To help illustrate the crawling examples we have created a sample website at http://example.webscraping.com. The source code used to generate this website is available at http://bitbucket.org/WebScrapingWithPython/website, which includes instructions how to host the website yourself if you prefer.

We decided to build a custom website for the examples instead of scraping live websites so we have full control over the environment. This provides us stability - live websites are updated more often than books and by the time you try a scraping example it may no longer work. Also a custom website allows us to craft examples that illustrate specific skills and avoid distractions. Finally a live website might not appreciate us using them to learn about web scraping and might then block our scrapers. Using our own custom website avoids these risks, however the skills learnt in these examples can certainly still be applied to live websites.

Who this book is for

This book assumes prior programming experience and would most likely not be suitable for absolute beginners. The web scraping examples require competence with Python and installing modules with pip. If you need a brush-up there is an excellent free online book by Mark Pilgrim available at http://www.diveintopython.net. This is the resource I originally used to learn Python.

The examples also assume knowledge of how webpages are constructed with HTML and updated with JavaScript. Prior knowledge of HTTP, CSS, AJAX, WebKit, and Redis would also be useful but not required, and will be introduced as each technology is needed. Detailed references for many of these topics are available at https://developer.mozilla.org/.

Conventions

In this book, you will find a number of styles of text that distinguish between different kinds of information. Here are some examples of these styles, and an explanation of their meaning.

Code words in text are shown as follows: "We can include other contexts through the use of the include directive."

A block of code is set as follows:

from urllib.request import urlopen
from urllib.error import URLError

url = 'http://example.webscraping.com'
try:
    html = urlopen(url).read()
except urllib2.URLError as e:
    html = None

Any command-line input or output is written as follows:

python script.py

We will occasionally show Python interpreter prompts used by the normal Python interpreter, such as:

>>> import urllib

Or the IPython interpreter, such as:

In [1]: import urllib

New terms and important words are shown in bold. Words that you see on the screen, in menus or dialog boxes for example, appear in the text like this: "clicking the Next button moves you to the next screen".

Note

Warnings or important notes appear in a box like this.

Note

Tips and tricks appear like this.

 

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