JSON responses with jsonify in Flask - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ component_behavior

intermediate

What is the output of this Flask route using jsonify?

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 An HTML page showing the dictionary

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

D A Python dictionary {'name': 'Alice', 'age': 30}

💡 Hint

jsonify converts Python dicts into JSON strings with correct content-type.

The jsonify function converts the Python dictionary into a JSON string and sets the response content-type to application/json. So the client receives JSON text, not a Python dict or HTML.

🔧 Debug

intermediate

Which option causes a TypeError in Flask jsonify usage?

Which of these Flask route return statements will cause a TypeError?

Flask

from flask import jsonify

@app.route('/test')
def test():
    # return statement options below

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

B )}eurT :'dilav'{(yfinosj nruter

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

D return jsonify({'valid': True,})

💡 Hint

jsonify returns a Response object, you cannot add strings to it.

Option A tries to concatenate a string to the Response object returned by jsonify, which causes a TypeError at runtime because Response objects do not support string concatenation. Options B, C, and D are valid.

❓ state_output

advanced

What is the Content-Type header of this Flask jsonify response?

Given this Flask route, what is the Content-Type header sent to the client?

Flask

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

@app.route('/info')
def info():
    return jsonify({'status': 'ok'})

A application/json

B text/html; charset=utf-8

C application/json; charset=utf-8

D text/plain

💡 Hint

jsonify sets content-type to JSON with UTF-8 charset.

The jsonify function sets the Content-Type header to application/json; charset=utf-8 by default to indicate JSON data encoded in UTF-8.

🔧 Debug

advanced

Why does this Flask jsonify call raise a TypeError?

Examine this code snippet. Why does it raise a TypeError when the route is accessed?

Flask

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

@app.route('/error')
def error():
    data = {'time': set([1, 2, 3])}
    return jsonify(data)

A Missing return statement causes error

B Sets are not JSON serializable, causing TypeError

C jsonify requires a list, not a dict

D Flask app is not created properly

💡 Hint

Check if all data types in the dictionary can be converted to JSON.

The set type is not supported by JSON serialization. When jsonify tries to convert the dictionary, it raises a TypeError because sets cannot be converted to JSON.

🧠 Conceptual

expert

Which option correctly returns a JSON response with a custom status code using jsonify?

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

Flask

from flask import jsonify

@app.route('/create')
def create():
    data = {'message': 'Created successfully'}
    # return statement options below

A return jsonify(data).with_status(201)

B return jsonify(data, status=201)

C return jsonify(data).status_code(201)

D return jsonify(data), 201

💡 Hint

Flask routes can return a tuple with response and status code.

To set a custom status code with jsonify, return a tuple: (jsonify(data), status_code). Options B, C, and D are invalid syntax or methods.