Accessing JSON data in Flask - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ component_behavior

intermediate

What is the output of this Flask route when sending JSON data?

Consider this Flask route that receives JSON data and returns a value from it. What will be the response if the client sends {"name": "Alice", "age": 30} as JSON?

Flask

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

@app.route('/user', methods=['POST'])
def user():
    data = request.get_json()
    return jsonify({'greeting': f"Hello, {data['name']}!"})

A {"greeting": "Hello, 30!"}

B {"greeting": "Hello, None!"}

C KeyError exception

D {"greeting": "Hello, Alice!"}

💡 Hint

Look at how the JSON data is accessed by key 'name' in the dictionary.

The route uses request.get_json() to parse the JSON body into a dictionary. Then it accesses data['name'], which is 'Alice', and returns it in the greeting.

📝 Syntax

intermediate

Which option correctly accesses nested JSON data in Flask?

Given JSON data {"user": {"id": 5, "info": {"email": "[e-mail]"}}}, which code correctly extracts the email inside a Flask route?

Flask

data = request.get_json()
email = ???

A data['user']['info']['email']

B data['user']['email']

C data['info']['email']

D data['email']

💡 Hint

Follow the nested keys step by step from the JSON structure.

The email is nested inside 'user' then 'info', so you must access data['user']['info']['email']. Other options miss levels or keys.

🔧 Debug

advanced

Why does this Flask route raise an error when accessing JSON data?

This route tries to get a JSON key but raises an error. What is the cause?

Flask

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

@app.route('/data', methods=['POST'])
def data():
    data = request.json
    return data['key']

A KeyError because 'key' does not exist in data

B request.json is None if Content-Type is not application/json

C SyntaxError due to missing parentheses

D TypeError because data is a string

💡 Hint

Check the request headers and how Flask parses JSON automatically.

If the client does not send Content-Type: application/json, request.json returns None, so accessing data['key'] causes a TypeError. The error is due to request.json being None.

❓ state_output

advanced

What is the output of this Flask route when JSON data is missing a key?

Given this route, what happens if the client sends JSON {"name": "Bob"} but the code tries to access 'age'?

Flask

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

@app.route('/info', methods=['POST'])
def info():
    data = request.get_json()
    age = data['age']
    return jsonify({'age': age})

A {"age": 0}

B {"age": null}

C KeyError exception

D {"age": ""}

💡 Hint

What happens when you access a dictionary key that does not exist?

Accessing a missing key with data['age'] raises a KeyError. To avoid this, use data.get('age') or check key existence.

🧠 Conceptual

expert

Which option best explains how Flask handles JSON data in requests?

When a Flask route uses request.get_json(), what does Flask do internally to provide the JSON data?

A Flask reads the request body, checks Content-Type header, and parses JSON into a Python dict

B Flask requires manual parsing of JSON using json.loads(request.data)

C Flask uses the URL parameters to build JSON data

D Flask automatically converts all request data into JSON regardless of Content-Type

💡 Hint

Think about how Flask knows when to parse JSON and what it returns.

Flask checks if Content-Type is application/json, then parses the request body JSON into a Python dictionary returned by get_json(). It does not parse JSON automatically if the header is missing.