How to make an API using FastAPI

Let’s see how we can create a basic API using the FastAPI framework.

First, make sure you have FastAPI and Uvicorn installed. You can install them using:

As the FastAPI documentation suggests you'll need Uvicorn and FastAPI installed you can do so by:

pip install fastapi uvicorn[standard]

Now, let’s create a simple FastAPI application where we’ll be setting up our FastAPI app. Create a file named main.py:

# main.py
from fastapi import FastAPI

app = FastAPI()

But that’s not all we’re just initializing our FastAPI instance, now we also need to setup something known as CORS (Cross-Origin Resource Sharing).

CORS is important when you want to allow your API to be accessed by web applications from different origins. Modify your main.py file.

# main.py
from fastapi import FastAPI
from fastapi.middleware.cors import CORSMiddleware

app = FastAPI()

# Configure CORS

origins = ["http://localhost", "http://localhost:3000", "https://yourfrontenddomain.com"]

app.add_middleware(
    CORSMiddleware,
    allow_origins=origins,
    allow_credentials=True,
    allow_methods=["*"],
    allow_headers=["*"],
)

Replace the allowed origins (origins) with the actual domains of your front-end applications. Or if you’re just testing your app on localhost then you might not need to change much…

Make an API.

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

Your file should look like this.

# main.py
from fastapi import FastAPI
from fastapi.middleware.cors import CORSMiddleware

app = FastAPI()

# Configure CORS

origins = ["http://localhost", "http://localhost:3000", "https://yourfrontenddomain.com"]

app.add_middleware(
    CORSMiddleware,
    allow_origins=origins,
    allow_credentials=True,
    allow_methods=["*"],
    allow_headers=["*"],
)

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

Call your API of endpoint /. But before that we’ll need to start running the server. Now use the Uvicorn to initiate the FastAPI server.

uvicorn main:app --reload

This will start the FastAPI development server, and your API will be accessible at http://127.0.0.1:8000. The CORS middleware will allow requests from the specified origins.

You can access the API by opening your browser or using a tool like curl or Postman. For example, if you’re running it locally, open http://localhost:8000 in your browser, and you should see the “Hello, World!” message.

Hope this was useful. Thanks for reading.