Learning Objectives

By the end of this chapter, you will be able to:

• Replicate the concepts of RESTful API
• Describe the meaning of different HTTP methods and statuses
• Get hands-on experience on PyCharm IDE
• Build a RESTful API and execute CRUD using Flask
• Use JSON messages to communicate with the APIs
• Test API endpoints using Postman and httpie/curl command-line tools

This chapter introduces API and explains the concepts of web services, API and REST.

We are in the internet era, a world where everything is connected. Data flows seamlessly from one place to another. We can get all the information in the world with a few clicks on a website. Take Skyscanner as an example, we just need to put in the date and location of our trips, and it can find us the cheapest flight in a split second; the hero behind the scenes that provides this data is API.

In this chapter, you will learn what a web service, an API, and REST are. We will start by teaching the fundamental concepts of APIs. Then we will look at real-life examples of how different web services (Google, Facebook, and so on) use the REST API.

Finally, we will develop our first simple Python RESTful API using Python. Python is a popular and powerful programming language. Apart from its extensive use in the realm of artificial intelligence, it is also widely used in web application development, big data analysis, web scraping, and process automation. What makes Python excel in so many areas is the extensive number of frameworks available. The frameworks do all the heavy lifting jobs and that allows the developers to focus on the actual application design and development.

In this chapter, you will see how data is encoded and communicated between the frontend and the backend. You will learn technical details about the JSON format, the HTTP protocol, HTTP status codes, and so on. All the development work will be verified and tested using Postman and httpie/curl. We will take you through the whole process of web application development. Not only will you learn the essential aspects of developing a RESTful API, but you will also learn about the thinking process, design, development, testing, and even deployment. This is a journey of learning the complete software development life cycle. Let's embark on our exciting journey now!

API stands for application programming interface; it is an interface for the website (or mobile application) to communicate with the backend logic. Simply put, it is like a messenger that takes a request from the users and sends the request to the backend system. Once the backend system responds, it will then pass that response to the users. A metaphor for this is a waiter/waitress, who can understand different customers' orders. They will then act as a middleman between the customers and the chefs in the kitchen.

If you were the boss of the restaurant, the key benefit of having a waiter/waitress here between your customer and the kitchen is that the customers will be shielded from seeing your business secrets. They don't need to know how the meal is prepared. They just need to send an order through the waiter/waitress, and they will get the meal they ordered. In this scenario, the waiter acts like the API. The following figure helps illustrate the analogy.

Figure 1.1: The waiter acting as the API for the customer

Similarly, in computer science, one of the key benefits of having API is encapsulation. We encapsulate the logic so that people outside won't be able to see it. With this arrangement, big companies with sensitive information are willing to provide services to the world through APIs, confident that their internal information won't be revealed. Take Skyscanner again as an example. The company is comfortable with using an API to allow customers to book their flights, but at the same time, personal data from other customers that are stored in their internal database won't leak.

An API is also a standard interface that can communicate with different types of frontend Terminals, they can be mobile applications or websites. As long as the frontend is sending the same request to the API, it will get the same result back. If we go back to our metaphor, the waiter/waitress will serve all kinds of customers, regardless of their gender, age, language, and so on.

Now, imagine you are a software engineer at Skyscanner who is responsible for developing an API. What will your job be? Let me tell you. Your job will be to write a program that can take booking requests (date and location) from customers through the website, and then look up matching flights in the Skyscanner database and return the flight details to the customers. Throughout this book, you will be our API engineering intern. We will guide you, step by step, through the process of developing a RESTful API project that can serve the users of your system.