HTTP methods (GET, POST, PUT, DELETE) in Flask - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ component_behavior

intermediate

What is the output of this Flask route when accessed with a GET request?

Consider this Flask route:

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

@app.route('/data', methods=['GET', 'POST'])
def data():
    if request.method == 'POST':
        return 'Posted Data'
    else:
        return 'Got Data'

What will the server respond with when a GET request is sent to /data?

Flask

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

@app.route('/data', methods=['GET', 'POST'])
def data():
    if request.method == 'POST':
        return 'Posted Data'
    else:
        return 'Got Data'

A The response will be 'Posted Data'

B The response will be 'Got Data'

C The server will return a 405 Method Not Allowed error

D The server will return a 404 Not Found error

💡 Hint

Think about which method triggers which return statement.

The route accepts both GET and POST. When the method is GET, the else branch runs, returning 'Got Data'.

📝 Syntax

intermediate

Which Flask route definition correctly handles PUT requests?

Choose the correct Flask route decorator to handle PUT requests on the path /update.

A @app.route('/update', methods=['PUT'])

B @app.route('/update', methods='PUT')

C @app.route('/update', method='PUT')

D @app.route('/update', methods=['put'])

💡 Hint

Check the spelling and type of the methods argument.

The methods argument must be a list of uppercase HTTP method strings. Option A is correct.

🔧 Debug

advanced

What error does this Flask route raise when accessed with DELETE?

Given this Flask route:

@app.route('/item', methods=['GET', 'POST'])
def item():
    return 'Item endpoint'

What happens if a client sends a DELETE request to /item?

Flask

@app.route('/item', methods=['GET', 'POST'])
def item():
    return 'Item endpoint'

A The server returns a 404 Not Found error

B The server raises a TypeError

C The server returns 'Item endpoint'

D The server returns a 405 Method Not Allowed error

💡 Hint

Check which methods are allowed by the route.

The route only allows GET and POST. DELETE is not allowed, so Flask returns a 405 error.

❓ state_output

advanced

What is the final value of the list after these HTTP requests?

Consider this Flask app snippet:

from flask import Flask, request
app = Flask(__name__)
items = []

@app.route('/add', methods=['POST'])
def add():
    items.append(request.json.get('item'))
    return 'Added'

If the client sends these requests in order:

1. POST to /add with JSON {"item": "apple"}
2. POST to /add with JSON {"item": "banana"}
3. GET to /add

What is the value of items after these requests?

Flask

from flask import Flask, request
app = Flask(__name__)
items = []

@app.route('/add', methods=['POST'])
def add():
    items.append(request.json.get('item'))
    return 'Added'

A ['apple', 'banana']

B ['apple']

C []

D ['banana']

💡 Hint

Remember that GET requests to this route are not handled.

Both POST requests add items to the list. The GET request does nothing to the list because it is not handled.

🧠 Conceptual

expert

Which HTTP method is idempotent and safe according to REST principles?

In REST API design, which HTTP method is considered both idempotent and safe?

A PUT

B POST

C GET

D DELETE

💡 Hint

Safe means it does not change server state. Idempotent means multiple identical requests have the same effect as one.

GET requests do not change data (safe) and can be repeated without side effects (idempotent). POST is not idempotent or safe. PUT and DELETE are idempotent but not safe.

Practice

1. Which HTTP method is typically used in Flask to retrieve data without changing anything on the server?

easy

A. PUT

B. POST

C. GET

D. DELETE

Solution

1. Step 1: Understand HTTP methods purpose

   GET is used to request data without modifying it, so it is safe and idempotent.

2. Step 2: Match method to Flask usage

   In Flask, GET routes are used to send data back to the client without changing server state.

3. Final Answer:

   GET -> Option C

4. Quick Check:

   Retrieve data = GET [OK]

Hint: GET reads data, POST creates, PUT updates, DELETE removes [OK]

Common Mistakes:

• Confusing POST with GET for data retrieval
• Using DELETE to get data
• Thinking PUT is for reading data

2. Which of the following Flask route definitions correctly allows handling both GET and POST methods?

easy

A. @app.route('/submit', allow_methods=['GET', 'POST'])

B. @app.route('/submit', methods=['GET', 'POST'])

C. @app.route('/submit', methods='GET, POST')

D. @app.route('/submit', method=['GET', 'POST'])

Solution

1. Step 1: Recall Flask route syntax for methods

   Flask uses the 'methods' keyword argument as a list of strings to specify allowed HTTP methods.

2. Step 2: Check each option's syntax

   @app.route('/submit', methods=['GET', 'POST']) correctly uses methods=['GET', 'POST']. Others have wrong keywords or wrong data types.

3. Final Answer:

   @app.route('/submit', methods=['GET', 'POST']) -> Option B

4. Quick Check:

   Correct keyword and list format = @app.route('/submit', methods=['GET', 'POST']) [OK]

Hint: Use methods=['GET', 'POST'] exactly in route decorator [OK]

Common Mistakes:

• Using 'method' instead of 'methods'
• Passing methods as a string instead of list
• Using unknown keywords like 'allow_methods'

3. What will be the output when a client sends a DELETE request to this Flask route?

@app.route('/item/', methods=['DELETE'])
def delete_item(id):
    return f"Deleted item {id}", 200

medium

A. "Deleted item <id>" with status 200

B. 404 Not Found error

C. Method Not Allowed error

D. Empty response with status 204

Solution

1. Step 1: Analyze route and method

   The route accepts DELETE requests with an integer id parameter and returns a string with status 200.

2. Step 2: Understand response for DELETE request

   Since the method matches and function returns a message with 200, the client receives that message and status.

3. Final Answer:

   "Deleted item <id>" with status 200 -> Option A

4. Quick Check:

   DELETE request handled correctly = "Deleted item <id>" with status 200 [OK]

Hint: Route method matches request method, so response is returned [OK]

Common Mistakes:

• Expecting 404 if route exists
• Confusing DELETE with GET behavior
• Assuming empty response without checking code

4. Identify the error in this Flask route that should handle PUT requests:

@app.route('/update', methods=['PUT'])
def update():
    data = request.get_json()
    return 'Updated', 200

medium

A. Missing import of 'request' from Flask

B. Incorrect HTTP method name 'PUT'

C. Route decorator syntax is invalid

D. Function must return JSON, not string

Solution

1. Step 1: Check usage of 'request'

   The function uses 'request.get_json()' but 'request' is not imported from Flask, causing a NameError.

2. Step 2: Verify other parts

   Method 'PUT' is valid, route syntax is correct, and returning string with status 200 is allowed.

3. Final Answer:

   Missing import of 'request' from Flask -> Option A

4. Quick Check:

   Using 'request' without import causes error [OK]

Hint: Always import 'request' to access request data [OK]

Common Mistakes:

• Forgetting to import 'request'
• Thinking PUT is invalid method
• Assuming string return is wrong

5. You want to create a Flask API endpoint to update a user's email using PUT and delete the user using DELETE at the same URL '/user/'. Which is the best way to define this in Flask?

hard

A. Use GET method for both update and delete actions

B. Create two separate routes with different URLs for PUT and DELETE

C. Use only POST method and check a hidden field for action

D. Use one route with methods=['PUT', 'DELETE'] and check request.method inside the function

Solution

1. Step 1: Understand RESTful design

   PUT and DELETE are standard methods for update and delete at the same resource URL.

2. Step 2: Implement in Flask

   Flask allows one route to handle multiple methods; inside the function, you check request.method to run correct code.

3. Final Answer:

   Use one route with methods=['PUT', 'DELETE'] and check request.method inside the function -> Option D

4. Quick Check:

   Multiple methods on one route with method check = Use one route with methods=['PUT', 'DELETE'] and check request.method inside the function [OK]

Hint: One route, multiple methods, check request.method inside [OK]

Common Mistakes:

• Creating separate URLs for same resource actions
• Using POST or GET incorrectly for update/delete
• Not checking request.method inside route