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Downloading HTML with Python

In this lesson we'll start building a Python application for watching prices. As a first step, we'll use the HTTPX library to download HTML code of a product listing page.

Using browser tools for developers is crucial for understanding the structure of a particular page, but it's a manual task. Let's start building our first automation, a Python program which downloads HTML code of the product listing.

Starting a Python project​

Before we start coding, we need to set up a Python project. Create new directory with a virtual environment, then inside the directory and with the environment activated, install the HTTPX library:

$ pip install httpx
...
Successfully installed ... httpx-0.0.0
Installing packages

Being comfortable around Python project setup and installing packages is a prerequisite of this course, but if you wouldn't say no to a recap, we recommend the Installing Packages tutorial from the official Python Packaging User Guide.

Now let's test that all works. Inside the project directory create a new file called main.py with the following code:

import httpx

print("OK")

Running it as a Python program will verify that your setup is okay and you've installed HTTPX:

$ python main.py
OK
Troubleshooting

If you see errors or for any other reason cannot run the code above, it means that your environment isn't set up correctly. We're sorry, but figuring out the issue is out of scope of this course.

Downloading product listing​

Now onto coding! Let's change our code so it downloads HTML of the product listing instead of printing OK. The documentation of the HTTPX library provides us with examples how to use it. Inspired by those, our code will look like this:

import httpx

url = "https://warehouse-theme-metal.myshopify.com/collections/sales"
response = httpx.get(url)
print(response.text)

If you run the program now, it should print the downloaded HTML:

$ python main.py
<!doctype html>
<html class="no-js" lang="en">
  <head>
    <meta charset="utf-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0, height=device-height, minimum-scale=1.0, maximum-scale=1.0">
    <meta name="theme-color" content="#00badb">
    <meta name="robots" content="noindex">
    <title>Sales</title>
  ...
  </body>
</html>

Running httpx.get(url), we made a HTTP request and received a response. It's not particularly useful yet, but it's a good start of our scraper.

Client and server, request and response

HTTP is a network protocol powering the internet. Understanding it well is an important foundation for successful scraping, but for this course, it's enough to know just the basic flow and terminology:

  • HTTP is an exchange between two participants.
  • The client sends a request to the server, which replies with a response.
  • In our case, main.py is the client, and the technology running at warehouse-theme-metal.myshopify.com replies to our request as the server.

Handling errors​

Websites can return various errors, such as when the server is temporarily down, applying anti-scraping protections, or simply being buggy. In HTTP, each response has a three-digit status code that indicates whether it is an error or a success.

All status codes

If you've never worked with HTTP response status codes before, briefly scan their full list to get at least a basic idea of what you might encounter. For further education on the topic, we recommend HTTP Cats as a highly professional resource.

A robust scraper skips or retries requests on errors. Given the complexity of this task, it's best to use libraries or frameworks. For now, we'll at least make sure that our program visibly crashes and prints what happened in case there's an error.

First, let's ask for trouble. We'll change the URL in our code to a page that doesn't exist, so that we get a response with status code 404. This could happen, for example, when the product we are scraping is no longer available:

https://warehouse-theme-metal.myshopify.com/does/not/exist

We could check the value of response.status_code against a list of allowed numbers, but HTTPX already provides response.raise_for_status(), a method that analyzes the number and raises the httpx.HTTPError exception if our request wasn't successful:

import httpx

url = "https://warehouse-theme-metal.myshopify.com/does/not/exist"
response = httpx.get(url)
response.raise_for_status()
print(response.text)

If you run the code above, the program should crash:

$ python main.py
Traceback (most recent call last):
  File "/Users/.../main.py", line 5, in <module>
    response.raise_for_status()
  File "/Users/.../.venv/lib/python3/site-packages/httpx/_models.py", line 761, in raise_for_status
    raise HTTPStatusError(message, request=request, response=self)
httpx.HTTPStatusError: Client error '404 Not Found' for url 'https://warehouse-theme-metal.myshopify.com/does/not/exist'
For more information check: https://developer.mozilla.org/en-US/docs/Web/HTTP/Status/404

Letting our program visibly crash on error is enough for our purposes. Now, let's return to our primary goal. In the next lesson, we'll be looking for a way to extract information about products from the downloaded HTML.

Exercises​

These challenges are here to help you test what you’ve learned in this lesson. Try to resist the urge to peek at the solutions right away. Remember, the best learning happens when you dive in and do it yourself!

Real world

You're about to touch the real web, which is practical and exciting! But websites change, so some exercises might break. If you run into any issues, please leave a comment below or file a GitHub Issue.

Scrape AliExpress​

Download HTML of a product listing page, but this time from a real world e-commerce website. For example this page with AliExpress search results:

https://www.aliexpress.com/w/wholesale-darth-vader.html
Solution
import httpx

url = "https://www.aliexpress.com/w/wholesale-darth-vader.html"
response = httpx.get(url)
response.raise_for_status()
print(response.text)

Save downloaded HTML as a file​

Download HTML, then save it on your disk as a products.html file. You can use the URL we've been already playing with:

https://warehouse-theme-metal.myshopify.com/collections/sales
Solution

Right in your Terminal or Command Prompt, you can create files by redirecting output of command line programs:

python main.py > products.html

If you want to use Python instead, it offers several ways how to create files. The solution below uses pathlib:

import httpx
from pathlib import Path

url = "https://warehouse-theme-metal.myshopify.com/collections/sales"
response = httpx.get(url)
response.raise_for_status()
Path("products.html").write_text(response.text)

Download an image as a file​

Download a product image, then save it on your disk as a file. While HTML is textual content, images are binary. You may want to scan through the HTTPX QuickStart for guidance. You can use this URL pointing to an image of a TV:

https://warehouse-theme-metal.myshopify.com/cdn/shop/products/sonyxbr55front_f72cc8ff-fcd6-4141-b9cc-e1320f867785.jpg
Solution

Python offers several ways how to create files. The solution below uses pathlib:

from pathlib import Path
import httpx

url = "https://warehouse-theme-metal.myshopify.com/cdn/shop/products/sonyxbr55front_f72cc8ff-fcd6-4141-b9cc-e1320f867785.jpg"
response = httpx.get(url)
response.raise_for_status()
Path("tv.jpg").write_bytes(response.content)