HTTP status codes for APIs in Flask - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to return a 200 OK status in a Flask API response.

Flask

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

@app.route('/status')
def status():
    return jsonify({'message': 'Success'}), [1]

Drag options to blanks, or click blank then click option'

A200

B301

C500

D404

Attempts:

3 left

💡 Hint

Common Mistakes

Using 404 which means Not Found

Using 500 which means Server Error

The HTTP status code 200 means the request was successful.

2fill in blank

medium

Complete the code to return a 404 Not Found status when a resource is missing.

Flask

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

@app.route('/item/<int:id>')
def get_item(id):
    item = None  # pretend we looked for the item
    if not item:
        return jsonify({'error': 'Item not found'}), [1]

Drag options to blanks, or click blank then click option'

A404

B400

C201

D403

Attempts:

3 left

💡 Hint

Common Mistakes

Using 201 which means Created

Using 400 which means Bad Request

404 means the requested resource was not found on the server.

3fill in blank

hard

Fix the error in the code to return a 201 Created status after adding a new resource.

Flask

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

@app.route('/add', methods=['POST'])
def add_item():
    data = request.json
    # pretend we add the item here
    return jsonify({'message': 'Item added'}), [1]

Drag options to blanks, or click blank then click option'

A400

B200

C201

D500

Attempts:

3 left

💡 Hint

Common Mistakes

Using 200 which means OK but not specific for creation

Using 400 which means Bad Request

201 means a new resource was successfully created.

4fill in blank

hard

Fill both blanks to return a 400 Bad Request status with a JSON error message.

Flask

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

@app.route('/submit', methods=['POST'])
def submit():
    data = request.json
    if not data or 'name' not in data:
        return jsonify({'error': [1]), [2]

Drag options to blanks, or click blank then click option'

A'Missing name field'

B400

C200

D'Success'

Attempts:

3 left

💡 Hint

Common Mistakes

Using 200 which means OK

Using a success message instead of an error

400 means the client sent a bad request. The error message explains the problem.

5fill in blank

hard

Fill all three blanks to return a 403 Forbidden status with a JSON error message and a custom header.

Flask

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

@app.route('/admin')
def admin():
    response = make_response(jsonify({'error': [1]), [2])
    response.headers['X-Reason'] = [3]
    return response

Drag options to blanks, or click blank then click option'

A'Access denied'

B403

C'User not authorized'

D200

Attempts:

3 left

💡 Hint

Common Mistakes

Using 200 which means OK

Using wrong or missing error messages

403 means the user is forbidden from accessing the resource. The JSON and header explain why.

Practice

1. What HTTP status code should a Flask API return when a request is successful and data is sent back?

easy

A. 200 OK

B. 404 Not Found

C. 500 Internal Server Error

D. 201 Created

Solution

1. Step 1: Understand the meaning of status codes

   200 means the request was successful and the server is returning the requested data.

2. Step 2: Match the code to the scenario

   Since the request succeeded and data is returned, 200 OK is the correct code.

3. Final Answer:

   200 OK -> Option A

4. Quick Check:

   Success response = 200 OK [OK]

Hint: Success with data? Use 200 OK [OK]

Common Mistakes:

• Confusing 201 Created with simple success
• Using 404 when resource exists
• Using 500 for client errors

2. Which of the following is the correct way to return a JSON response with a 201 status code in Flask?

easy

A. return data, code=201

B. return data, status=201

C. return json.dumps(data), 201

D. return jsonify(data), 201

Solution

1. Step 1: Recall Flask's return syntax for JSON and status

   Flask uses jsonify() to convert data to JSON and returns a tuple (response, status_code).

2. Step 2: Identify the correct syntax

   return jsonify(data), 201 correctly uses jsonify(data), 201 to return JSON with status 201.

3. Final Answer:

   return jsonify(data), 201 -> Option D

4. Quick Check:

   Flask JSON + status = jsonify(data), 201 [OK]

Hint: Use jsonify() and return tuple (data, status) [OK]

Common Mistakes:

• Using json.dumps without jsonify
• Incorrect keyword arguments like status= or code=
• Returning raw data without JSON conversion

3. Consider this Flask route code:

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

@app.route('/item/')
def get_item(id):
    items = {1: 'apple', 2: 'banana'}
    if id in items:
        return jsonify({'item': items[id]}), 200
    else:
        return jsonify({'error': 'Item not found'}), 404

What HTTP status code will be returned when accessing /item/3?

medium

A. 200

B. 404

C. 500

D. 201

Solution

1. Step 1: Check if id 3 exists in items dictionary

   Items only have keys 1 and 2, so 3 is not found.

2. Step 2: Identify the returned status code for missing item

   The else block returns 404 Not Found with an error message.

3. Final Answer:

   404 -> Option B

4. Quick Check:

   Missing resource = 404 Not Found [OK]

Hint: Missing item? Return 404 Not Found [OK]

Common Mistakes:

• Assuming 200 even if item missing
• Confusing 404 with 500 server error
• Returning 201 for missing resource

4. This Flask API code is intended to return a 400 Bad Request if the 'name' field is missing in JSON input:

@app.route('/add', methods=['POST'])
def add():
    data = request.get_json()
    if 'name' not in data:
        return {'error': 'Name required'}, 400
    return {'message': 'Added'}, 201

What is the main problem with this code?

medium

A. It returns a dict instead of using jsonify

B. It returns 201 instead of 200 on success

C. It does not import request from flask

D. It uses wrong status code for missing name

Solution

1. Step 1: Check imports needed for request

   The code uses request.get_json() but does not show importing request from flask.

2. Step 2: Identify the error caused by missing import

   Without importing request, the code will raise a NameError at runtime.

3. Final Answer:

   It does not import request from flask -> Option C

4. Quick Check:

   Missing import request causes error [OK]

Hint: Always import request to use request.get_json() [OK]

Common Mistakes:

• Ignoring missing imports causing runtime errors
• Thinking returning dict is invalid (Flask accepts dict)
• Confusing 201 Created as wrong success code here

5. You want to create a Flask API endpoint that creates a new user. If the username already exists, return 400 Bad Request. If creation succeeds, return 201 Created with the new user's ID. Which code snippet correctly implements this behavior?

hard

A. def create_user():
data = request.get_json()
if data['username'] in users:
return {'error': 'User exists'}, 400
new_id = len(users) + 1
users[new_id] = data['username']
return {'id': new_id}, 201

B. def create_user():
data = request.get_json()
if data['username'] in users:
return {'error': 'User exists'}, 404
new_id = len(users) + 1
users[new_id] = data['username']
return {'id': new_id}, 200

C. def create_user():
data = request.get_json()
if data['username'] in users:
return {'error': 'User exists'}, 500
new_id = len(users) + 1
users[new_id] = data['username']
return {'id': new_id}, 201

D. def create_user():
data = request.get_json()
if data['username'] in users:
return {'error': 'User exists'}, 201
new_id = len(users) + 1
users[new_id] = data['username']
return {'id': new_id}, 400

Solution

1. Step 1: Check status code for existing user

   400 Bad Request is correct when username already exists, indicating client error.

2. Step 2: Check status code for successful creation

   201 Created is the correct code for successful resource creation.

3. Step 3: Verify code matches these codes

   def create_user(): data = request.get_json() if data['username'] in users: return {'error': 'User exists'}, 400 new_id = len(users) + 1 users[new_id] = data['username'] return {'id': new_id}, 201 returns 400 for existing user and 201 for success, matching requirements.

4. Final Answer:

   Option A code snippet -> Option A

5. Quick Check:

   Existing user = 400, success = 201 [OK]

Hint: Use 400 for bad input, 201 for successful creation [OK]

Common Mistakes:

• Using 404 or 500 for existing user error
• Returning 200 instead of 201 on creation
• Mixing up success and error codes