With Python tools like Beautiful Soup, you can scrape and parse this data directly from web pages to use for your projects and applications. Let's use the example of scraping MIDI data from the internet to train a neural network with Magenta that can generate classic Nintendo-sounding music. Nov 19, 2020 One can easily download the web directories by iterating recursively through the website! This is a browser-independent method and much faster! One can simply scrape a web page to get all the file URLs on a webpage and hence, download all files in a single command-Implementing Web Scraping in Python with BeautifulSoup. Apr 25, 2020 Web mining module for Python, with tools for scraping, natural language processing, machine learning, network analysis and visualization. clips/pattern. Check out the tutorial on how to scrape dynamic web pages with Python. Learn how to extract data with Selenium, headless browsers, and the web scraping API.
Once you’ve put together enough web scrapers, you start to feel like you can do it in your sleep. I’ve probably built hundreds of scrapers over the years for my own projects, as well as for clients and students in my web scraping course.
Occasionally though, I find myself referencing documentation or re-reading old code looking for snippets I can reuse. One of the students in my course suggested I put together a “cheat sheet” of commonly used code snippets and patterns for easy reference.
I decided to publish it publicly as well – as an organized set of easy-to-reference notes – in case they’re helpful to others.
While it’s written primarily for people who are new to programming, I also hope that it’ll be helpful to those who already have a background in software or python, but who are looking to learn some web scraping fundamentals and concepts.
Table of Contents:
- Extracting Content from HTML
- Storing Your Data
- More Advanced Topics
Useful Libraries
For the most part, a scraping program deals with making HTTP requests and parsing HTML responses.
I always make sure I have requests and BeautifulSoup installed before I begin a new scraping project. From the command line:
Then, at the top of your .py file, make sure you’ve imported these libraries correctly.
Making Simple Requests
Make a simple GET request (just fetching a page)
Make a POST requests (usually used when sending information to the server like submitting a form)
Pass query arguments aka URL parameters (usually used when making a search query or paging through results)
Inspecting the Response
See what response code the server sent back (useful for detecting 4XX or 5XX errors)
Access the full response as text (get the HTML of the page in a big string)
Look for a specific substring of text within the response
Check the response’s Content Type (see if you got back HTML, JSON, XML, etc)
Extracting Content from HTML
Now that you’ve made your HTTP request and gotten some HTML content, it’s time to parse it so that you can extract the values you’re looking for.
Using Regular Expressions
Using Regular Expressions to look for HTML patterns is famously NOT recommended at all.
However, regular expressions are still useful for finding specific string patterns like prices, email addresses or phone numbers.
Run a regular expression on the response text to look for specific string patterns:
Using BeautifulSoup
BeautifulSoup is widely used due to its simple API and its powerful extraction capabilities. It has many different parser options that allow it to understand even the most poorly written HTML pages – and the default one works great.
Compared to libraries that offer similar functionality, it’s a pleasure to use. To get started, you’ll have to turn the HTML text that you got in the response into a nested, DOM-like structure that you can traverse and search
Look for all anchor tags on the page (useful if you’re building a crawler and need to find the next pages to visit)
Look for all tags with a specific class attribute (eg <li>..</li>)
Look for the tag with a specific ID attribute (eg: <div>..</div>) Reason 7 free download mac.
Look for nested patterns of tags (useful for finding generic elements, but only within a specific section of the page)
Look for all tags matching CSS selectors (similar query to the last one, but might be easier to write for someone who knows CSS)
Get a list of strings representing the inner contents of a tag (this includes both the text nodes as well as the text representation of any other nested HTML tags within)
Return only the text contents within this tag, but ignore the text representation of other HTML tags (useful for stripping our pesky <span>, <strong>, <i>, or other inline tags that might show up sometimes)
Convert the text that are extracting from unicode to ascii if you’re having issues printing it to the console or writing it to files
Get the attribute of a tag (useful for grabbing the src attribute of an <img> tag or the href attribute of an <a> tag)
Putting several of these concepts together, here’s a common idiom: iterating over a bunch of container tags and pull out content from each of them
Using XPath Selectors
BeautifulSoup doesn’t currently support XPath selectors, and I’ve found them to be really terse and more of a pain than they’re worth. I haven’t found a pattern I couldn’t parse using the above methods.
If you’re really dedicated to using them for some reason, you can use the lxml library instead of BeautifulSoup, as described here.
Storing Your Data
Now that you’ve extracted your data from the page, it’s time to save it somewhere.
Note: The implication in these examples is that the scraper went out and collected all of the items, and then waited until the very end to iterate over all of them and write them to a spreadsheet or database.
I did this to simplify the code examples. In practice, you’d want to store the values you extract from each page as you go, so that you don’t lose all of your progress if you hit an exception towards the end of your scrape and have to go back and re-scrape every page.
Writing to a CSV
Probably the most basic thing you can do is write your extracted items to a CSV file. By default, each row that is passed to the csv.writer object to be written has to be a python list.
In order for the spreadsheet to make sense and have consistent columns, you need to make sure all of the items that you’ve extracted have their properties in the same order. This isn’t usually a problem if the lists are created consistently.
If you’re extracting lots of properties about each item, sometimes it’s more useful to store the item as a python dict instead of having to remember the order of columns within a row. The csv module has a handy DictWriter that keeps track of which column is for writing which dict key.
Writing to a SQLite Database
You can also use a simple SQL insert if you’d prefer to store your data in a database for later querying and retrieval.
More Advanced Topics
These aren’t really things you’ll need if you’re building a simple, small scale scraper for 90% of websites. But they’re useful tricks to keep up your sleeve.
Javascript Heavy Websites
Contrary to popular belief, you do not need any special tools to scrape websites that load their content via Javascript. In order for the information to get from their server and show up on a page in your browser, that information had to have been returned in an HTTP response somewhere.
It usually means that you won’t be making an HTTP request to the page’s URL that you see at the top of your browser window, but instead you’ll need to find the URL of the AJAX request that’s going on in the background to fetch the data from the server and load it into the page.
There’s not really an easy code snippet I can show here, but if you open the Chrome or Firefox Developer Tools, you can load the page, go to the “Network” tab and then look through the all of the requests that are being sent in the background to find the one that’s returning the data you’re looking for. Start by filtering the requests to only XHR or JS to make this easier.
Once you find the AJAX request that returns the data you’re hoping to scrape, then you can make your scraper send requests to this URL, instead of to the parent page’s URL. If you’re lucky, the response will be encoded with JSON which is even easier to parse than HTML.
Content Inside Iframes
This is another topic that causes a lot of hand wringing for no reason. Sometimes the page you’re trying to scrape doesn’t actually contain the data in its HTML, but instead it loads the data inside an iframe.
Again, it’s just a matter of making the request to the right URL to get the data back that you want. Make a request to the outer page, find the iframe, and then make another HTTP request to the iframe’s src attribute.
Sessions and Cookies
While HTTP is stateless, sometimes you want to use cookies to identify yourself consistently across requests to the site you’re scraping.
The most common example of this is needing to login to a site in order to access protected pages. Without the correct cookies sent, a request to the URL will likely be redirected to a login form or presented with an error response.
However, once you successfully login, a session cookie is set that identifies who you are to the website. As long as future requests send this cookie along, the site knows who you are and what you have access to.
Delays and Backing Off
If you want to be polite and not overwhelm the target site you’re scraping, you can introduce an intentional delay or lag in your scraper to slow it down
Some also recommend adding a backoff that’s proportional to how long the site took to respond to your request. That way if the site gets overwhelmed and starts to slow down, your code will automatically back off.
Spoofing the User Agent
Beautiful Soup Python
By default, the requests library sets the User-Agent header on each request to something like “python-requests/2.12.4”. You might want to change it to identify your web scraper, perhaps providing a contact email address so that an admin from the target website can reach out if they see you in their logs.
More commonly, this is used to make it appear that the request is coming from a normal web browser, and not a web scraping program.
Using Proxy Servers
Even if you spoof your User Agent, the site you are scraping can still see your IP address, since they have to know where to send the response.
If you’d like to obfuscate where the request is coming from, you can use a proxy server in between you and the target site. The scraped site will see the request coming from that server instead of your actual scraping machine.
If you’d like to make your requests appear to be spread out across many IP addresses, then you’ll need access to many different proxy servers. You can keep track of them in a list and then have your scraping program simply go down the list, picking off the next one for each new request, so that the proxy servers get even rotation.
Setting Timeouts
If you’re experiencing slow connections and would prefer that your scraper moved on to something else, you can specify a timeout on your requests.
Handling Network Errors
Just as you should never trust user input in web applications, you shouldn’t trust the network to behave well on large web scraping projects. Eventually you’ll hit closed connections, SSL errors or other intermittent failures.
Learn More
If you’d like to learn more about web scraping, I currently have an ebook and online course that I offer, as well as a free sandbox website that’s designed to be easy for beginners to scrape.
Web Scraping Python Beautifulsoup Example
You can also subscribe to my blog to get emailed when I release new articles.
The internet has an amazingly wide variety of information for human consumption. But this data is often difficult to access programmatically if it doesn't come in the form of a dedicated REST API. With Python tools like Beautiful Soup, you can scrape and parse this data directly from web pages to use for your projects and applications.
Let's use the example of scraping MIDI data from the internet to train a neural network with Magenta that can generate classic Nintendo-sounding music. In order to do this, we'll need a set of MIDI music from old Nintendo games. Using Beautiful Soup we can get this data from the Video Game Music Archive.
Getting started and setting up dependencies
Before moving on, you will need to make sure you have an up to date version of Python 3 and pip installed. Make sure you create and activate a virtual environment before installing any dependencies.
You'll need to install the Requests library for making HTTP requests to get data from the web page, and Beautiful Soup for parsing through the HTML.
With your virtual environment activated, run the following command in your terminal:
We're using Beautiful Soup 4 because it's the latest version and Beautiful Soup 3 is no longer being developed or supported.
Using Requests to scrape data for Beautiful Soup to parse
First let's write some code to grab the HTML from the web page, and look at how we can start parsing through it. The following code will send a GET request to the web page we want, and create a BeautifulSoup object with the HTML from that page:
With this soup object, you can navigate and search through the HTML for data that you want. For example, if you run soup.title after the previous code in a Python shell you'll get the title of the web page. If you run print(soup.get_text()), you will see all of the text on the page.
Getting familiar with Beautiful Soup
The find() and find_all() methods are among the most powerful weapons in your arsenal. soup.find() is great for cases where you know there is only one element you're looking for, such as the body tag. On this page, soup.find(id='banner_ad').text will get you the text from the HTML element for the banner advertisement.
soup.find_all() is the most common method you will be using in your web scraping adventures. Using this you can iterate through all of the hyperlinks on the page and print their URLs:
You can also provide different arguments to find_all, such as regular expressions or tag attributes to filter your search as specifically as you want. You can find lots of cool features in the documentation.
Parsing and navigating HTML with BeautifulSoup
Before writing more code to parse the content that we want, let’s first take a look at the HTML that’s rendered by the browser. Every web page is different, and sometimes getting the right data out of them requires a bit of creativity, pattern recognition, and experimentation.
Our goal is to download a bunch of MIDI files, but there are a lot of duplicate tracks on this webpage as well as remixes of songs. We only want one of each song, and because we ultimately want to use this data to train a neural network to generate accurate Nintendo music, we won't want to train it on user-created remixes.
When you're writing code to parse through a web page, it's usually helpful to use the developer tools available to you in most modern browsers. If you right-click on the element you're interested in, you can inspect the HTML behind that element to figure out how you can programmatically access the data you want.
Let's use the find_all method to go through all of the links on the page, but use regular expressions to filter through them so we are only getting links that contain MIDI files whose text has no parentheses, which will allow us to exclude all of the duplicates and remixes.
Create a file called nes_midi_scraper.py and add the following code to it:
This will filter through all of the MIDI files that we want on the page, print out the link tag corresponding to them, and then print how many files we filtered.
Run the code in your terminal with the command python nes_midi_scraper.py.
Downloading the MIDI files we want from the webpage
Now that we have working code to iterate through every MIDI file that we want, we have to write code to download all of them.
In nes_midi_scraper.py, add a function to your code called download_track, and call that function for each track in the loop iterating through them:
In this download_track function, we're passing the Beautiful Soup object representing the HTML element of the link to the MIDI file, along with a unique number to use in the filename to avoid possible naming collisions.
Run this code from a directory where you want to save all of the MIDI files, and watch your terminal screen display all 2230 MIDIs that you downloaded (at the time of writing this). This is just one specific practical example of what you can do with Beautiful Soup.
The vast expanse of the World Wide Web
Now that you can programmatically grab things from web pages, you have access to a huge source of data for whatever your projects need. One thing to keep in mind is that changes to a web page’s HTML might break your code, so make sure to keep everything up to date if you're building applications on top of this.
If you're looking for something to do with the data you just grabbed from the Video Game Music Archive, you can try using Python libraries like Mido to work with MIDI data to clean it up, or use Magenta to train a neural network with it or have fun building a phone number people can call to hear Nintendo music.
I’m looking forward to seeing what you build. Feel free to reach out and share your experiences or ask any questions.
- Email: sagnew@twilio.com
- Twitter: @Sagnewshreds
- Github: Sagnew
- Twitch (streaming live code): Sagnewshreds