API error handling in Flask - Mini Project: Build & Apply

API Error Handling in Flask

📖 Scenario: You are building a simple Flask API that returns user data. Sometimes, the user ID requested might not exist. You want to handle this error gracefully and return a clear message with the right HTTP status code.

🎯 Goal: Create a Flask API with a route /user/<int:user_id> that returns user data if found. If the user ID does not exist, return a JSON error message with status code 404 using Flask's error handling.

📋 What You'll Learn

Create a dictionary called users with these exact entries: 1: {'name': 'Alice', 'age': 30}, 2: {'name': 'Bob', 'age': 25}, 3: {'name': 'Charlie', 'age': 35}

Create a Flask app instance called app

Add a route /user/<int:user_id> that returns user data as JSON if found

If the user ID is not found, raise a NotFound exception

Add an error handler for NotFound that returns a JSON response with {'error': 'User not found'} and status code 404

💡 Why This Matters

🌍 Real World

APIs often need to handle errors gracefully to give clear feedback to users or client apps. This project shows how to do that in Flask.

💼 Career

Knowing how to handle API errors properly is essential for backend developers and anyone building web services.

1

Create the user data dictionary

Create a dictionary called users with these exact entries: 1: {'name': 'Alice', 'age': 30}, 2: {'name': 'Bob', 'age': 25}, 3: {'name': 'Charlie', 'age': 35}

Flask

# Create the users dictionary with exact entries
# Your code here

Need a hint?

Use a dictionary with integer keys and dictionary values for user info.

2

Create the Flask app instance

Import Flask from flask and create a Flask app instance called app

Flask

users = {
    1: {'name': 'Alice', 'age': 30},
    2: {'name': 'Bob', 'age': 25},
    3: {'name': 'Charlie', 'age': 35}
}

# Import Flask and create app instance
# Your code here

Need a hint?

Use app = Flask(__name__) to create the app instance.

3

Add the user route with error raising

Import jsonify and abort from flask. Add a route /user/<int:user_id> to app that returns the user data as JSON if found in users. If not found, use abort(404) to raise a 404 error.

Flask

from flask import Flask

users = {
    1: {'name': 'Alice', 'age': 30},
    2: {'name': 'Bob', 'age': 25},
    3: {'name': 'Charlie', 'age': 35}
}

app = Flask(__name__)

# Import jsonify and abort
# Add route /user/ that returns user data or aborts 404
# Your code here

Need a hint?

Use @app.route decorator and abort(404) to handle missing users.

4

Add error handler for 404 Not Found

Import NotFound from werkzeug.exceptions. Add an error handler for NotFound to app that returns a JSON response {'error': 'User not found'} with status code 404.

Flask

from flask import Flask, jsonify, abort

users = {
    1: {'name': 'Alice', 'age': 30},
    2: {'name': 'Bob', 'age': 25},
    3: {'name': 'Charlie', 'age': 35}
}

app = Flask(__name__)

@app.route('/user/')
def get_user(user_id):
    if user_id in users:
        return jsonify(users[user_id])
    else:
        abort(404)

# Import NotFound and add error handler for it
# Your code here

Need a hint?

Use @app.errorhandler(NotFound) decorator and return JSON with status 404.