HTTPException usage in FastAPI - Mini Project: Build & Apply

Using HTTPException in FastAPI

📖 Scenario: You are building a simple FastAPI web service that returns user information. You want to handle cases where the requested user does not exist by sending a proper HTTP error response.

🎯 Goal: Create a FastAPI app with a route /users/{user_id} that returns user data if found. If the user ID is not in the data, raise an HTTPException with status code 404 and a clear error message.

📋 What You'll Learn

Create a dictionary called users with these exact entries: 1: {'name': 'Alice'}, 2: {'name': 'Bob'}, 3: {'name': 'Charlie'}

Create a FastAPI app instance called app

Create a GET route /users/{user_id} that accepts an integer user_id

Inside the route, check if user_id is in users

If user_id is not found, raise HTTPException(status_code=404, detail='User not found')

If found, return the user data dictionary for that user_id

💡 Why This Matters

🌍 Real World

Web APIs often need to handle missing data gracefully by sending proper HTTP error codes and messages.

💼 Career

Knowing how to use HTTPException in FastAPI is essential for backend developers building robust APIs.

1

Create the user data dictionary

Create a dictionary called users with these exact entries: 1: {'name': 'Alice'}, 2: {'name': 'Bob'}, 3: {'name': 'Charlie'}

FastAPI

# Create the users dictionary with user IDs and names
# Your code here

Need a hint?

Use curly braces to create a dictionary. Keys are numbers 1, 2, 3. Values are dictionaries with key 'name' and the exact names.

2

Create the FastAPI app instance

Import FastAPI from fastapi and create an app instance called app by calling FastAPI()

FastAPI

users = {
    1: {'name': 'Alice'},
    2: {'name': 'Bob'},
    3: {'name': 'Charlie'}
}

# Import FastAPI and create app instance
# Your code here

Need a hint?

Use from fastapi import FastAPI and then app = FastAPI() to create the app.

3

Create the GET route with user_id parameter

Import HTTPException from fastapi. Create a GET route /users/{user_id} using @app.get. Define a function get_user that takes an integer parameter user_id. Inside the function, check if user_id is in users. If not, raise HTTPException(status_code=404, detail='User not found'). If found, return users[user_id].

FastAPI

from fastapi import FastAPI
from fastapi import HTTPException

users = {
    1: {'name': 'Alice'},
    2: {'name': 'Bob'},
    3: {'name': 'Charlie'}
}

app = FastAPI()

# Create GET route /users/{user_id} with function get_user(user_id: int)
# Check if user_id in users, else raise HTTPException
# Return users[user_id] if found
# Your code here

Need a hint?

Use @app.get('/users/{user_id}') to create the route. Use if user_id not in users: to check. Raise HTTPException with status 404 and detail message if missing.

4

Complete the FastAPI app with proper imports and route

Ensure the code imports FastAPI and HTTPException from fastapi. The app instance is called app. The GET route /users/{user_id} is defined with function get_user(user_id: int). The function raises HTTPException(status_code=404, detail='User not found') if the user is missing, else returns the user data from users dictionary.

FastAPI

from fastapi import FastAPI
from fastapi import HTTPException

users = {
    1: {'name': 'Alice'},
    2: {'name': 'Bob'},
    3: {'name': 'Charlie'}
}

app = FastAPI()

@app.get('/users/{user_id}')
def get_user(user_id: int):
    if user_id not in users:
        raise HTTPException(status_code=404, detail='User not found')
    return users[user_id]

# Final check: all imports, app, route, and exception usage are correct
# Your code here

Need a hint?

Review your code to confirm all parts are present and correct.