JSON request parsing in Flask - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ component_behavior

intermediate

What is the output of this Flask route when receiving a JSON POST?

Consider this Flask route that expects JSON data with a key 'name'. What will be the response if the client sends {"name": "Alice"} as JSON?

Flask

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

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

A KeyError

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

C {"message": "Hello, Alice!"}

D TypeError

💡 Hint

Look at how request.get_json() extracts the JSON body and how the 'name' key is accessed.

The route uses request.get_json() to parse the JSON body. Since the client sends {"name": "Alice"}, data['name'] is 'Alice'. The response JSON contains the greeting message with 'Alice'.

📝 Syntax

intermediate

Which option correctly parses JSON from a Flask request?

You want to parse JSON data sent in a POST request in Flask. Which code snippet correctly gets the JSON data?

A data = request.json()

B data = request.get_json()

C data = request.get_json

D data = request.json

💡 Hint

Remember that get_json is a method you need to call.

request.get_json() is the correct method call to parse JSON data from the request body. request.json is a property but may not always parse correctly. request.json() is invalid syntax. request.get_json without parentheses is a method object, not the result.

🔧 Debug

advanced

Why does this Flask route raise a TypeError when parsing JSON?

Given this Flask route, why does it raise a TypeError when a client sends JSON data?

Flask

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

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

A request.get_json is a method, missing parentheses causes TypeError when subscripted

B request.get_json returns None because no JSON sent

C KeyError because 'key' does not exist in JSON

D SyntaxError due to missing colon

💡 Hint

Check how request.get_json is used in the code.

The code assigns request.get_json (the method itself) to json_data without calling it. Then it tries to subscript it with ['key'], causing a TypeError because a method object is not subscriptable.

❓ state_output

advanced

What is the value of 'user' after this Flask route processes JSON?

In this Flask route, what will be the value of the variable 'user' after parsing the JSON body {"user": {"id": 5, "name": "Bob"}}?

Flask

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

@app.route('/user', methods=['POST'])
def user_route():
    data = request.get_json()
    user = data.get('user', {})
    return user

A {"id": 5, "name": "Bob"}

B "user"

C {}

D None

💡 Hint

Look at how data.get('user', {}) works when the key exists.

data.get('user', {}) returns the value associated with 'user' key in the JSON, which is {"id": 5, "name": "Bob"}.

🧠 Conceptual

expert

What error occurs if Flask receives invalid JSON with request.get_json()?

If a Flask route calls request.get_json() but the client sends malformed JSON, what error will Flask raise?

A ValueError

B KeyError

C TypeError

D werkzeug.exceptions.BadRequest

💡 Hint

Think about how Flask handles bad requests and JSON parsing errors.

When request.get_json() tries to parse invalid JSON, Flask raises a werkzeug.exceptions.BadRequest error indicating the client sent bad data.