Scrape Static Websites

Say that you want to capture and analyze data from a website. Of course, you could simply copy-paste the data from each page but you would quickly run into issues. What if the data on the page gets updated (i.e., would you have time available to copy-paste the new data, too)? Or what if there are simply so many pages that you can’t possibly do it all by hand (i.e., thousands of product pages)?

Web scraping can help you overcome these issues by programmatically grabbing data from the web. The tools best suited for the job depend on the type of website: static or dynamic. In this building block, we focus on static websites, which always return the same information.

Code

Requests

Each site is made up of HTML code that you can view with, for example, Google Inspector. This source code contains data about the look and feel and contents of a website. To store the source code of a website in Python, you can use the get() method from the requests package, while for R, the rvest package is employed for the same purpose:

		
import requests

url = "https://www.abcdefhijklmnopqrstuvwxyz.nl"

# make a get request to the URL
request_object = requests.get(url)

# return the source code from the request object
source_code = request_object.text
#install.packages("rvest")
library(rvest)

url = "https://www.abcdefhijklmnopqrstuvwxyz.nl"

# read the html from the URL
source_code = read_html(url)

Seed Generation

In practice, you typically scrape data from a multitude of links (also known as the seed). Each URL has a fixed and variable part. The latter may be a page number that increases by increments of 1 (e.g., page-1, page-2). The code snippet below provides an example of how you can quickly generate such a list of URLs.

		
base_url = # the fixed part of the URL
num_pages = # the number of pages you want to scrape
page_urls = []

for counter in range(1, num_pages+1):
  full_url = base_url + "page-" + str(counter) + ".html"
  page_urls.append(full_url)
base_url = # the fixed part of the URL
num_pages = # the number of pages you want to scrape
page_urls = character(num_pages)

for (i in 1:num_pages) {
	page_urls[i] = paste0(base_url,"page-",i)}

Tip

Rather than inserting a fixed number of pages (num_pages), you may want to leverage the page navigation menu instead. For example, you could extract the next page url (if it exists) from a “Next” button.

Beautifulsoup

Next, once we have imported the source_code, it is a matter of extracting specific elements. The BeautifulSoup package has several built-in methods that simplify this process significantly. Moreover, the rvest package in R provides tools and functions that allow you to extract data from HTML and XML documents, making it easier to gather information from websites.

Finding content in a website’s source code

The .find() and .find_all() methods search for matching HTML elements (e.g., h1 is a header). While .find() always prints out the first matching element, find_all() captures all of them and returns them as a list. Often, you are specifically interested in the text you have extracted and less so in the HTML tags. To get rid of them, you can use the .get_text() method.

In R, when using the rvest package, an equivalent approach involves the html_elements method. To access the text content without the HTML tags, you can further apply the html_text() function.

		
from bs4 import BeautifulSoup

soup = BeautifulSoup(source_code, "html.parser")

# the first matching <h1> element
print(soup.find('h1'))

# all matching <h2> elements (returns a list of elements)
print(soup.find_all('h1'))

# first element in in the list
print(soup.find_all('h2')[0])

# strip HTML tags from element
print(soup.find_all('h2')[0].get_text())
# the first matching <h1> element
html_element(source_code,'h1')

# all matching <h2> elements (returns a list of elements)
html_elements(source_code,'h2')

# first elementin in the list
html_elements(source_code,'h2')[1]

# strip HTML tags from element
html_text(html_elements(source_code,'h2')[1])

Tip

In practice, you often find yourself in situations that require chaining one or more commands, for example soup.find('table').find_all('tr')[1].find('td') looks for the first column (td) of the second row (tr) in the table.

Selectors

Rather than searching by HTML tag, you can specify which elements to extract through attributes, classes, and identifiers:

		
# element attributes
soup.find("a").attrs["href"]

# HTML classes (note the underscore after class!)
soup.find(class_ = "<CLASS_NAME>")

# HTML identifiers
soup.find(id = "<ID_NAME>")
# element attributes
html_attr(html_elements(source_code,"a"),"href")

# HTML classes (note the . before the class name)
html_elements(source_code,".<CLASS_NAME>")

# HTML identifiers
html_elements(source_code,"#<ID_NAME>>")

Tip

You can combine HTML tags and selectors like this:
soup.find("h1", class_ = "menu-header"]

Advanced Use Case

Task Scheduling

See the building block on task automation on how to schedule the execution of the web scraper (e.g., every day). Keep in mind that this only works with Python scripts, so if you’re currently working in a Jupyter Notebook you need to transform it into a .py file first.

Scrape Static Websites