Flask route as API endpoint - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ component_behavior

intermediate

What is the output of this Flask API endpoint?

Consider this Flask route that returns JSON data. What will the client receive when accessing /api/data?

Flask

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

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

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

B <Response 200 OK>

C name: Alice, age: 30

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

💡 Hint

Think about what jsonify does and what format the client receives.

The jsonify function converts the dictionary into a JSON string with correct content-type. The client receives a JSON string, not a Python dict or a plain string.

📝 Syntax

intermediate

Which Flask route definition will cause a syntax error?

Identify the Flask route decorator that will cause a syntax error when defining an API endpoint.

A

@app.route('/api/user')
def user():
return 'User data'

B

@app.route('/api/user')
def user():
    return 'User data'

C

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D

@app.route('/api/user')
def user():
    return {'user': 'Bob'}

💡 Hint

Check the indentation of the function body.

Option A lacks indentation for the return statement, causing an IndentationError in Python.

❓ state_output

advanced

What is the response status code of this Flask API endpoint?

Given this Flask route, what status code will the client receive when accessing /api/status?

Flask

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

@app.route('/api/status')
def status():
    return jsonify({'status': 'ok'}), 201

A 201

B 500

C 404

D 200

💡 Hint

Look at the second value returned by the function.

Returning a tuple with (response, status_code) sets the HTTP status code. Here it is 201 Created.

🔧 Debug

advanced

Why does this Flask API endpoint raise a TypeError?

Examine the code below. Why will calling /api/error cause a TypeError?

Flask

from flask import Flask
app = Flask(__name__)

@app.route('/api/error')
def error():
    return {'message': 'fail'}

A Route decorator syntax is invalid

B Missing return statement causes NoneType error

C Flask cannot convert dict to response automatically without jsonify

D Function name 'error' is reserved and causes conflict

💡 Hint

Flask needs a proper response object or string, not a raw dict.

Returning a dict directly without jsonify causes Flask to raise a TypeError because it cannot convert dict to a valid response.

🧠 Conceptual

expert

Which option correctly implements a Flask API endpoint that accepts a URL parameter and returns it in JSON?

You want to create an API endpoint /api/item/<id> that returns the id parameter as JSON. Which code snippet does this correctly?

A

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

@app.route('/api/item/<id>')
def item():
    return jsonify({'id': id})

B

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

@app.route('/api/item/<id>')
def item(id):
    return jsonify({'id': id})

C

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

@app.route('/api/item/<int:id>')
def item(id):
    return {'id': id}

D

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

@app.route('/api/item/<int:id>')
def item():
    return jsonify({'id': id})

💡 Hint

Check the function parameters and route variable types carefully.

Option B correctly defines the route with a string parameter and passes it to the function. It returns JSON using jsonify. Option B misses the id parameter in the function. Option B misses the id parameter and will cause a NameError. Option B returns a dict without jsonify, causing a TypeError.

Practice

1. What does a Flask route do in a web application?

easy

A. It styles the webpage with CSS.

B. It stores data in a database automatically.

C. It compiles Python code into machine code.

D. It defines a URL where the app listens for requests.

Solution

1. Step 1: Understand the role of a route

   A Flask route sets a specific web address that the app listens to for incoming requests.

2. Step 2: Identify what routes do not do

   Routes do not handle styling, database storage automatically, or code compilation.

3. Final Answer:

   It defines a URL where the app listens for requests. -> Option D

4. Quick Check:

   Flask route = URL listener [OK]

Hint: Routes map URLs to functions handling requests [OK]

Common Mistakes:

• Thinking routes handle styling or database storage
• Confusing routes with frontend design
• Assuming routes compile code

2. Which of the following is the correct syntax to create a Flask route for the URL '/api/data'?

easy

A. @app.route('/api/data')\ndef get_data():\n return 'data'

B. @app.route('/api/data')\nfunction get_data() { return 'data'; }

C. app.route('/api/data')\ndef get_data():\n return 'data'

D. @app.route('/api/data')\ndef get_data():\nprint('data')

Solution

1. Step 1: Check Flask route decorator syntax

   The correct syntax uses @app.route('/api/data') above a Python function definition.

2. Step 2: Verify function and return statement

   The function must be defined with def and return a value; print does not send a response.

3. Final Answer:

   @app.route('/api/data')\ndef get_data():\n return 'data' -> Option A

4. Quick Check:

   Python route decorator + def + return = D [OK]

Hint: Use @app.route decorator and def function with return [OK]

Common Mistakes:

• Using JavaScript syntax inside Flask route
• Missing @ before app.route
• Using print instead of return in route function

3. What will be the output when accessing the '/hello' route in this Flask app?

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

@app.route('/hello')
def hello():
    return jsonify({'message': 'Hello, world!'})

medium

A. {'message': 'Hello, world!'} as JSON response

B. Plain text: Hello, world!

C. HTML page with 'Hello, world!' text

D. Error: jsonify is not defined

Solution

1. Step 1: Understand jsonify usage

   The function returns jsonify({'message': 'Hello, world!'}), which sends a JSON response.

2. Step 2: Identify response type

   The response is JSON formatted, not plain text or HTML, and no error occurs because jsonify is imported.

3. Final Answer:

   {'message': 'Hello, world!'} as JSON response -> Option A

4. Quick Check:

   jsonify returns JSON response [OK]

Hint: jsonify returns JSON, not plain text or HTML [OK]

Common Mistakes:

• Confusing jsonify with print or return string
• Expecting HTML instead of JSON
• Forgetting to import jsonify

4. Identify the error in this Flask route code:

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

@app.route('/data')
def data():
    return json({'key': 'value'})

medium

A. Missing @ before app.route decorator

B. json is not imported or defined; should use jsonify

C. Function name 'data' is invalid

D. Route URL must start with '/api/'

Solution

1. Step 1: Check function return statement

   The code uses json({'key': 'value'}) but json is not imported or defined.

2. Step 2: Identify correct function for JSON response

   Flask provides jsonify to return JSON responses, which is imported here.

3. Final Answer:

   json is not imported or defined; should use jsonify -> Option B

4. Quick Check:

   Use jsonify, not json, for JSON response [OK]

Hint: Use jsonify, not json, to return JSON in Flask [OK]

Common Mistakes:

• Using json instead of jsonify
• Forgetting to import jsonify
• Assuming function names must follow special rules

5. You want to create a Flask API endpoint '/user/' that returns JSON with the user's id and a greeting message. Which code correctly implements this?

hard

A. @app.route('/user/')\ndef user():\n return jsonify({'id': id, 'message': 'Hello user'})

B. @app.route('/user/<id>')\ndef user(id):\n return {'id': id, 'message': 'Hello user ' + id}

C. @app.route('/user/')\ndef user(id):\n return jsonify({'id': id, 'message': f'Hello user {id}'})

D. @app.route('/user/')\ndef user(id):\n print({'id': id, 'message': f'Hello user {id}'})

Solution

1. Step 1: Check route URL and parameter type

   The route uses '/user/' which correctly captures an integer parameter named id.

2. Step 2: Verify function parameters and return

   The function accepts id and returns a JSON response using jsonify with the correct message format.

3. Step 3: Identify errors in other options

   @app.route('/user/<id>')\ndef user(id):\n return {'id': id, 'message': 'Hello user ' + id} misses int type and returns a dict without jsonify; @app.route('/user/')\ndef user():\n return jsonify({'id': id, 'message': 'Hello user'}) misses id parameter; @app.route('/user/')\ndef user(id):\n print({'id': id, 'message': f'Hello user {id}'}) uses print instead of return.

4. Final Answer:

   @app.route('/user/')\ndef user(id):\n return jsonify({'id': id, 'message': f'Hello user {id}'}) -> Option C

5. Quick Check:

   Route with int param + jsonify return = A [OK]

Hint: Use in route and return jsonify with id [OK]

Common Mistakes:

• Not specifying for integer parameter
• Returning dict without jsonify
• Using print instead of return in route