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(Image: Food.com)

What is Beautiful Soup? Something your mom makes for you on a cold January day? I hope so. Beautiful Soup is a webscraping Python library, and however difficult you thought webscraping would be, Beatiful Soup makes it so much easier. For instance, I used it on one project, when I had to scrape the Genius website, since their API doesn't actually provide song lyrics (I know right? You had one job, Genius).

Let's look at a sample technical interview question:

# Crawl a webpage and print the most common word with 
# the count of that word.

# Page to crawl:
# https://en.wikipedia.org/wiki/Apple_Inc.

# Only words from the section “history” should be accounted for.

# Example of the expected result
#     # of occurrences
# The 205

We're given Apple's Wikipedia page, and we want to find the most common word in the "history" section. So let's get started.

1. Setup and Installation

First we need to import Beautiful Soup. Install from the command line via pip3 install bs4 (or however you have pip configured). Check the documentation if you're having issues with installation.

Then, let's require our library at the top of the code. Here's everything we'll need:

from bs4 import BeautifulSoup, Tag
import requests

from collections import defaultdict

Next, we're ready to define our function.

def find_most_common():

2. Get the Page

Let's get our page and parse it with Beautiful soup. To get the page, we use the requests library:

  page = requests.get("https://en.wikipedia.org/wiki/Apple_Inc.")

Next, we parse the page text using Beautiful Soup.

  soup = BeautifulSoup(page.text, "html.parser")

How do we get just the history section? We have to take a look at the HTML of the page. There's a lot of random-looking gibberish, which I've tried to clean up:

<h2>
    <span class="mw-headline" id="History">History</span>
</h2>
<div ...>...</div>
<div ...>...</div>
<h3>
    <span ...></span>
    <span class="mw-headline" id="1976–1984:_Founding_and_incorporation">1976–1984: Founding and incorporation</span>
</h3>
.
.
.
<p>Apple Computer Company was founded on April 1, 1976, by <a href="/wiki/Steve_Jobs" title="Steve Jobs">Steve Jobs</a>...

For some reason, Wikipedia seems to have all their content in one div. This means that the "history" section is not its own div, but a header and some stuff inside a parent div, which contains all the sections. To get only the history section, the best we can do for now is to just grab that header and everything after it. We grab the <span> tag with ID "History", and then go to its parent, the <h2>. To get everything after it, we can use the BeautifulSoup notation, next_siblings. Altogether:

  history = soup.find(id="History").parent.next_siblings

3. Count the Words

Let's initialize a couple variables. We'll need the most common word and the number of times it appears. We'll also use a dictionary to store the count of each word. If you've been following this blog, you've probably guessed that we'll use a default dicitonary for this (if you don't remember, we can set the dictionary's default type to integers. That way, if we access a key that doesn't exist, the default value is already 0).

  max_count = 0
  max_word = ""
  dd = defaultdict(int)

Now, we're ready to crawl. Let's loop through history and look at each element, elem. However, Beautiful Soup sometimes returns something called a "Navigable String" instead of an element. We'll filter out everything that isn't an element using the isinstance() method from our library.

  for elem in history:
    if isinstance(elem, Tag):

Let's think of what happens next. We need to look at the text for each element in history, and count the instance of each word. However, remember, we need to stop when we're no longer in the history section. The next section is the same div, but starts with an <h2> tag. Then, we can end the function by printing the most common word and its count. I'll return max_count.

  for elem in history:
    if isinstance(elem, Tag):
      if elem.name == "h2":
        print(max_word, "is the most common, appearing", max_count, "times.")
        return max_count

But what if it's not the end of the section? We need to get the text by calling the BeautifulSoup get_text() method, and then split it into words by calling split() on each space.

      words = elem.get_text().split()

What's next? Loop through each word and update its count in the dictionary. Since we're using a default dictionary, we don't have to check to see if the word is already in there before adding 1 to it. Also, don't forget to update the max_word and max_count if we find a word that's more common than what we had previously.

      for word in words:
        dd[word] += 1
        if dd[word] > max_count:
          max_count = dd[word]
          max_word = word 

And that's it! The code should work...unless Wikipedia changes the layout of their site. Let's add a final check at the end in case that happens. Altogether:

from bs4 import BeautifulSoup, Tag
import requests

from collections import defaultdict

def find_most_common():
  page = requests.get("https://en.wikipedia.org/wiki/Apple_Inc.")
  soup = BeautifulSoup(page.text, "html.parser")
  history = soup.find(id="History").parent.next_siblings
  max_count = 0
  max_word = ""
  dd = defaultdict(int)

  for elem in history:
    if isinstance(elem, Tag):
      if elem.name == "h2":
        print(max_word, "is the most common, appearing", max_count, "times.")
        return max_count
      words = elem.get_text().split()
      for word in words:
        dd[word] += 1
        if dd[word] > max_count:
          max_count = dd[word]
          max_word = word

  return "Error"

Try it out

This function prints the result, so we can simply run it with find_most_common(). Running the code gives us the result:

the is the most common, appearing 328 times.

And there you have it! Granted, this function only works for this specific page, at the time of writing this--the main problem with web crawling is that it can break if the website owner alters their content in the slightest fashion. We also didn't account for casing or punctuation, something you may want to try and implement on your own. Just a few things to think about. See you next time!

< Week 17: Knapsack | View Solution on GitHub | Week 19: JS Array Functions >

Sheamus Heikkila is formerly a Teaching Assistant at General Assembly. This blog is not associated with GA.