API error handling in Flask - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ component_behavior

intermediate

What is the HTTP status code returned by this Flask error handler?

Consider this Flask code snippet that handles a 404 error. What HTTP status code will the client receive when this error handler is triggered?

Flask

from flask import Flask, jsonify
app = Flask(__name__)

@app.errorhandler(404)
def not_found(error):
    return jsonify({'error': 'Not found'}), 404

A 400

B 500

C 200

D 404

💡 Hint

Look at the second value returned in the tuple from the error handler.

The error handler returns a tuple with a JSON response and the status code 404, so the client receives a 404 status.

📝 Syntax

intermediate

Which option correctly raises a custom error with a JSON response in Flask?

You want to raise a 400 Bad Request error with a JSON message in Flask. Which code snippet correctly does this?

A

from flask import jsonify
return jsonify({'error': 'Bad request'}), 400

B

from flask import abort
abort(400, description={'error': 'Bad request'})

C

from flask import abort
abort(jsonify({'error': 'Bad request'}), 400)

D raise Exception(jsonify({'error': 'Bad request'}), 400)

💡 Hint

Flask's abort function does not accept a JSON object as description.

Option A returns a JSON response with status 400 correctly. Option A misuses abort with a dict description, C misuses abort with jsonify, and D raises a generic Exception which is not handled.

🔧 Debug

advanced

Why does this Flask error handler not return JSON as expected?

This Flask error handler is supposed to return JSON for 500 errors, but the client receives HTML instead. Why?

Flask

from flask import Flask, jsonify
app = Flask(__name__)

@app.errorhandler(500)
def internal_error(error):
    return {'error': 'Internal Server Error'}, 500

A The handler returns a dict, but Flask needs jsonify() to convert it to JSON response.

B The error handler must return a string, not a dict.

C The status code 500 is not allowed in error handlers.

D Flask automatically converts dict to JSON, so the problem is elsewhere.

💡 Hint

Check how Flask converts return values to responses.

Returning a dict alone does not produce a JSON response. Flask requires jsonify() to create a proper JSON response with correct headers.

❓ state_output

advanced

What is the output when a 403 error occurs with this Flask setup?

Given this Flask app, what JSON response does the client receive when a 403 Forbidden error is triggered?

Flask

from flask import Flask, jsonify
app = Flask(__name__)

@app.errorhandler(403)
def forbidden(error):
    response = jsonify({'message': 'Access denied'})
    response.status_code = 403
    return response

A {'error': 'Forbidden'} with HTTP status 403

B {'message': 'Access denied'} with HTTP status 403

C {'message': 'Access denied'} with HTTP status 200

D HTML error page with HTTP status 403

💡 Hint

Look at the JSON content and status code set in the response object.

The handler returns a JSON with key 'message' and sets status code 403 explicitly, so client gets that JSON and status 403.

🧠 Conceptual

expert

Which statement about Flask error handling is true?

Choose the correct statement about how Flask handles errors and error handlers.

A Flask automatically converts any returned dict from error handlers into JSON responses.

B Flask error handlers only work for HTTP errors raised by abort(), not for exceptions.

C Flask error handlers can catch exceptions globally and return custom responses for any HTTP status code.

D Flask requires error handlers to return plain strings, not JSON or response objects.

💡 Hint

Think about how Flask errorhandler decorator works with exceptions and HTTP codes.

Flask error handlers can catch exceptions or HTTP errors globally and return any custom response including JSON with any status code.