Custom response classes in FastAPI - Mini Project: Build & Apply

Custom Response Classes in FastAPI

📖 Scenario: You are building a simple FastAPI web service that returns different types of responses. You want to learn how to create and use custom response classes to control how your API sends data back to clients.

🎯 Goal: Build a FastAPI app that uses a custom response class to send plain text responses with a specific media type.

📋 What You'll Learn

Create a FastAPI app instance named app

Define a custom response class named PlainTextResponse that inherits from fastapi.responses.Response

Set the media type of PlainTextResponse to text/plain

Create a GET endpoint /hello that returns a PlainTextResponse with the text Hello, FastAPI!

💡 Why This Matters

🌍 Real World

Custom response classes let you control exactly how your API sends data back. This is useful when you want to send plain text, HTML, files, or other formats with specific headers.

💼 Career

Understanding custom response classes is important for backend developers working with FastAPI or similar frameworks to build APIs that meet client needs and standards.

1

Create the FastAPI app instance

Import FastAPI from fastapi and create an app instance called app.

FastAPI

from fastapi import FastAPI

# Create the FastAPI app instance
# Your code here

Need a hint?

Use app = FastAPI() to create the app instance.

2

Define a custom response class

Import Response from fastapi.responses and create a class called PlainTextResponse that inherits from Response. Set its media_type attribute to "text/plain".

FastAPI

from fastapi import FastAPI
from fastapi.responses import Response

app = FastAPI()

# Define the custom response class
# Your code here

Need a hint?

Define a class that inherits from Response and set media_type inside it.

3

Create a GET endpoint using the custom response

Create a GET endpoint at path /hello using @app.get("/hello"). Define a function called hello that returns a PlainTextResponse with the content "Hello, FastAPI!".

FastAPI

from fastapi import FastAPI
from fastapi.responses import Response

app = FastAPI()

class PlainTextResponse(Response):
    media_type = "text/plain"

# Create the GET endpoint
# Your code here

Need a hint?

Use @app.get("/hello") to create the route and return the custom response with the text.

4

Add response class to endpoint decorator

Modify the @app.get decorator on the hello function to include the parameter response_class=PlainTextResponse.

FastAPI

from fastapi import FastAPI
from fastapi.responses import Response

app = FastAPI()

class PlainTextResponse(Response):
    media_type = "text/plain"

# Modify the decorator to include response_class
# Your code here

Need a hint?

Add response_class=PlainTextResponse inside the @app.get decorator parentheses.