JSON response formatting in Flask - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ component_behavior

intermediate

What does this Flask route return as JSON?

Consider this Flask route code. What JSON response will the client receive when accessing /data?

Flask

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

@app.route('/data')
def data():
    return jsonify({'name': 'Alice', 'age': 30})

A '{"name": "Alice", "age": 30}'

B ["name", "Alice", "age", 30]

C {"name": "Alice", "age": 30}

D {name: Alice, age: 30}

💡 Hint

Remember that jsonify converts Python dicts to JSON strings with double quotes.

The jsonify function returns a JSON response with keys and string values in double quotes, matching option C exactly.

📝 Syntax

intermediate

Which option causes a syntax error in Flask JSON response?

Which Flask route code snippet will cause a syntax error when returning JSON?

Flask

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

@app.route('/test')
def test():
    # Choose the problematic return statement

A return jsonify({'valid': True})

B return jsonify({'missing_quote: True})

C return jsonify({'number': 123})

D return jsonify({'list': [1, 2, 3]})

💡 Hint

Look for missing or mismatched quotes in the dictionary keys or values.

Option B has a missing closing quote around the key 'missing_quote', causing a syntax error.

❓ state_output

advanced

What is the JSON output of this Flask route with nested data?

Given this Flask route, what JSON does it return?

Flask

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

@app.route('/nested')
def nested():
    data = {'user': {'id': 1, 'name': 'Bob'}, 'active': True}
    return jsonify(data)

A {"user": {"id": 1, "name": "Bob"}, "active": "true"}

B {"user": {"id": "1", "name": "Bob"}, "active": "True"}

C {"user": [1, "Bob"], "active": true}

D {"user": {"id": 1, "name": "Bob"}, "active": true}

💡 Hint

Boolean values in JSON are lowercase true/false, not strings.

Option D correctly shows nested objects and boolean true without quotes, matching Python dict to JSON conversion.

🔧 Debug

advanced

Why does this Flask JSON response raise a TypeError?

This Flask route raises a TypeError when returning JSON. Why?

Flask

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

class Custom:
    pass

@app.route('/error')
def error():
    obj = Custom()
    return jsonify({'obj': obj})

A Custom object is not JSON serializable

B Missing return statement

C Flask app not initialized

D jsonify requires a list, not dict

💡 Hint

Think about what types jsonify can convert to JSON.

jsonify cannot convert custom Python objects unless they are converted to JSON serializable types like dict or string.

🧠 Conceptual

expert

Which option correctly sets a custom HTTP status code with JSON response in Flask?

You want to return JSON data with a 201 Created status code. Which Flask return statement is correct?

Flask

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

@app.route('/create')
def create():
    data = {'message': 'Created successfully'}

A return jsonify(data), 201

B return jsonify(data, status=201)

C return jsonify(data).status_code(201)

D return jsonify(data).with_status(201)

💡 Hint

Flask allows returning a tuple with response and status code.

Returning (jsonify(data), 201) sets the response body and HTTP status code correctly.