When is web scraping useful?

Suppose I have a shop selling shoes and want to keep track of my competitor's prices. I could go to my competitor's website each day and compare each shoe's price with my own; however this will take a lot of time and will not scale well if I sell thousands of shoes or need to check price changes frequently. Or maybe I just want to buy a shoe when it's on sale. I could come back and check the shoe website each day until I get lucky, but the shoe I want might not be on sale for months. These repetitive manual processes could instead be replaced with an automated solution using the web scraping techniques covered in this book.

In an ideal world, web scraping wouldn't be necessary and each website would provide an API to share data in a structured format. Indeed, some websites do provide APIs, but they typically restrict the data that is available and how frequently it can be accessed. Additionally, a website developer might change, remove, or restrict the backend API. In short, we cannot rely on APIs to access the online data we may want. Therefore we need to learn about web scraping techniques.