Teaching FastAPI Python: Building a RESTful / WebAPI Step-by-Step

FastAPI is a modern web development framework for building APIs with Python. It is built on top of Starlette for the web parts and Pydantic for the data validation parts. FastAPI is well-known for its performance and ease of use, making it a popular choice for developers looking to create RESTful or Web APIs.

In this tutorial, we will guide you through how to create a RESTful API using FastAPI step-by-step. By the end of this tutorial, you will have a basic understanding of how FastAPI works and how to create a simple API with it.

Step 1: Setting Up

Before we start coding, let’s make sure you have FastAPI installed. You can install FastAPI using pip:

pip install fastapi

Next, we need to install the ASGI server, Uvicorn, which will run our FastAPI application:

pip install uvicorn

Step 2: Creating a FastAPI Application

Create a new Python file, let’s call it main.py, and start by importing FastAPI:

from fastapi import FastAPI

Next, create an instance of the FastAPI class:

app = FastAPI()

Step 3: Creating Endpoints

Now let’s create our first endpoint. An endpoint is a specific URI (Uniform Resource Identifier) that the API is located at. To create an endpoint, we will use the @app.get decorator provided by FastAPI. We will create a simple "Hello, World!" endpoint:

@app.get("/")
async def read_root():
    return {"message": "Hello, World!"}

In this endpoint, we are defining a GET method at the root URL ("/"). When a client sends a GET request to this endpoint, the function read_root will be executed, which will return a JSON response with the message "Hello, World!".

Step 4: Running the Application

To run our FastAPI application, we will use Uvicorn. In the terminal, navigate to the directory where main.py is located and run the following command:

uvicorn main:app --reload

This will start the Uvicorn server with main being the name of the Python file and app being the name of the FastAPI instance we created earlier. The --reload flag will automatically reload the server when the code changes.

Step 5: Testing the API

Open your web browser and go to http://localhost:8000/. You should see the "Hello, World!" message displayed in JSON format.

Congratulations! You have successfully created a simple RESTful API using FastAPI. This is just the tip of the iceberg when it comes to what FastAPI can do. It supports request validation, dependency injection, middleware, and many other features that make it a powerful tool for building APIs.

Feel free to experiment with FastAPI and explore its documentation to learn more about its capabilities. Happy coding!