Chapter 11. APIs

APIs (Application Programming Interfaces) are an important part of modern software engineering. You’ll find it very useful to know how to get data from an API and the basics of how they work. APIs allow two systems to communicate and transfer data. They can be exposed on the public internet or within a company’s internal systems. They hide the details of your code behind a standard way of accessing a system, providing a useful layer of abstraction. Many large software products use APIs to exchange data internally, and they’re particularly important in web development.

An API lets you programmatically access some data or perform some action. One of the first places you may come across an API is trying to download some data from a public API. If you send a request with a particular structure, you will get back what you are expecting. They are an example of client and server communications. The server sits and waits for something to contact it, and the client is the one doing the contacting. The client requests some data from the server, and the server shares that data. Web APIs generally use HTTP to make a request, then return a response as a JSON (JavaScript Object Notation) or XML file.

APIs are extremely useful because they can provide on-demand access to some data or functionality in a way that scales to large numbers of users. You might want to write your own API so that other systems can call your code without any action from you. A great example of this is ...

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