Custom status codes in Flask - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ component_behavior

intermediate

What is the HTTP status code returned by this Flask route?

Consider this Flask route that returns a custom status code.

What status code will the client receive when accessing this route?

Flask

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

@app.route('/custom')
def custom_status():
    return jsonify(message='Hello'), 202

# Assume app is running and /custom is accessed

A 202

B 404

C 200

D 500

💡 Hint

Look at the second value returned by the route function.

The route returns a tuple with the JSON response and the status code 202, so the client receives HTTP 202 Accepted.

📝 Syntax

intermediate

Which option correctly sets a custom status code in Flask?

You want to return a JSON response with a custom status code 418.
Which code snippet correctly does this?

A return jsonify(error='I am a teapot'), status=418

B return jsonify(error='I am a teapot', status=418)

C return jsonify(error='I am a teapot'), 418

D return jsonify(error='I am a teapot').status_code = 418

💡 Hint

Flask routes can return a tuple with response and status code.

Option C returns a tuple (response, status_code) which Flask understands. Other options either misuse parameters or syntax.

🔧 Debug

advanced

Why does this Flask route always return status 200 instead of 404?

Examine the code below:

```python @app.route('/item/') def get_item(id): item = find_item(id) if not item: return {'error': 'Not found'}, 404 return item ```
Despite returning 404 in the code, the client always receives 200. Why?

A The function returns a dict directly which Flask converts to 200, ignoring the tuple in the if block.

B The find_item function always returns a valid item, so 404 is never reached.

C Flask requires Response objects, not dicts, to set status codes.

D The route decorator is missing a methods argument, causing default 200.

💡 Hint

Check what the return type is in each branch.

Returning a dict directly sets status 200. The 404 tuple is only returned if item is None. If item is a dict, Flask returns 200 by default.

❓ state_output

advanced

What is the response status code after calling this Flask route twice?

Given this Flask app snippet:

```python from flask import Flask, jsonify app = Flask(__name__) counter = 0 @app.route('/count') def count(): global counter counter += 1 if counter > 1: return jsonify(message='Too many requests'), 429 return jsonify(message='First request'), 200 ```
What status code does the client receive on the second call to /count?

A 200

B 429

C 500

D 404

💡 Hint

Look at how the counter variable changes with each call.

On the first call, counter is 1, so status 200 is returned. On the second call, counter is 2, triggering status 429.

🧠 Conceptual

expert

Which statement about custom HTTP status codes in Flask is true?

Select the correct statement about using custom HTTP status codes in Flask responses.

A Flask automatically converts unknown status codes to 200 OK.

B Flask only supports standard HTTP status codes; custom codes cause errors.

C Custom status codes must be registered in Flask before use or they will raise exceptions.

D You can return any integer as a status code, but some clients may not recognize non-standard codes.

💡 Hint

Think about HTTP protocol and client behavior.

Flask allows any integer as status code, but clients may not handle unknown codes properly. Flask does not restrict codes or require registration.

Practice

1. What is the correct way to return a custom status code 450 from a Flask route?

easy

A. return "Error", 450

B. return 450, "Error"

C. return Response(status=450)

D. return make_response(450, "Error")

Solution

1. Step 1: Understand Flask return tuple format

   Flask routes return a tuple with (response_body, status_code) to set custom status codes.

2. Step 2: Match the tuple with custom code 450

   Returning "Error", 450 matches the format (body, status_code) correctly.

3. Final Answer:

   return "Error", 450 -> Option A

4. Quick Check:

   Tuple (body, status) = return "Error", 450 [OK]

Hint: Return (body, code) tuple to set custom status [OK]

Common Mistakes:

• Swapping order of status and body in return tuple
• Using Response without import or wrong parameters
• Using make_response incorrectly

2. Which of the following is the correct syntax to return a JSON response with a custom status code 499 in Flask?

easy

A. return jsonify(message="Fail"), 499

B. return jsonify(message="Fail", status=499)

C. return jsonify(message="Fail", 499)

D. return jsonify(message="Fail").status_code(499)

Solution

1. Step 1: Use jsonify to create JSON response

   jsonify returns a Response object with JSON content.

2. Step 2: Return tuple with jsonify and status code

   To set custom status code, return (jsonify(...), status_code) tuple.

3. Final Answer:

   return jsonify(message="Fail"), 499 -> Option A

4. Quick Check:

   jsonify + tuple (response, code) = return jsonify(message="Fail"), 499 [OK]

Hint: Return (jsonify(...), code) tuple for JSON + custom code [OK]

Common Mistakes:

• Passing status code inside jsonify arguments
• Trying to call status_code as method
• Incorrect tuple order or syntax

3. What will be the HTTP status code returned by this Flask route?

from flask import Flask
app = Flask(__name__)

@app.route('/test')
def test():
    return "Custom", 499

medium

A. 404

B. 200

C. 499

D. 500

Solution

1. Step 1: Check the return statement in route

   The route returns a tuple ("Custom", 499), where 499 is the status code.

2. Step 2: Flask uses the second tuple element as status code

   Flask sets HTTP status code to 499 as specified in the return tuple.

3. Final Answer:

   499 -> Option C

4. Quick Check:

   Return tuple second value = status code 499 [OK]

Hint: Second tuple value in return sets status code [OK]

Common Mistakes:

• Assuming default 200 status code
• Confusing return order
• Thinking 499 is invalid and defaults to 500

4. Identify the error in this Flask route that tries to return a custom status code 499:

from flask import Flask
app = Flask(__name__)

@app.route('/error')
def error():
    return "Oops", status=499

medium

A. Route function must return a Response object

B. Custom status code 499 is not allowed in Flask

C. Missing jsonify for JSON response

D. Using 'status' keyword argument in return is invalid

Solution

1. Step 1: Check return statement syntax

   Flask does not accept 'status' keyword in return statement directly.

2. Step 2: Correct way is to return tuple (body, status_code)

   Use return "Oops", 499 instead of return "Oops", status=499.

3. Final Answer:

   Using 'status' keyword argument in return is invalid -> Option D

4. Quick Check:

   Return tuple (body, code) not keyword args [OK]

Hint: Return tuple (body, code), not keyword args [OK]

Common Mistakes:

• Using status=code in return instead of tuple
• Assuming Flask auto-detects status from keywords
• Confusing with Response object parameters

5. You want to create a Flask route that returns a JSON message with a custom status code 460 only if a query parameter 'valid' is 'no'. Otherwise, return status 200 with a success message. Which code correctly implements this?

hard

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

@app.route('/check')
def check():
if request.args.get('valid') == 'no':
return jsonify(error="Invalid", status=460)
return jsonify(message="OK")

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

@app.route('/check')
def check():
if request.args.get('valid') == 'no':
return jsonify(error="Invalid"), 460
return jsonify(message="OK"), 200

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

@app.route('/check')
def check():
if request.args.get('valid') == 'no':
return jsonify(error="Invalid").status_code = 460
return jsonify(message="OK")

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

@app.route('/check')
def check():
if request.args.get('valid') == 'no':
return jsonify(error="Invalid")
return jsonify(message="OK"), 200

Solution

1. Step 1: Check conditional logic for query parameter

   Use request.args.get('valid') to check if it equals 'no'.

2. Step 2: Return JSON with custom status code 460 if invalid

   Return (jsonify(...), 460) tuple to set custom status code correctly.

3. Step 3: Return success JSON with status 200 otherwise

   Return (jsonify(...), 200) tuple for success response.

4. Final Answer:

   Correct conditional returns with tuples for custom and normal codes -> Option B

5. Quick Check:

   Return (jsonify, code) tuples for all cases [OK]

Hint: Return (jsonify(...), code) tuples for all responses [OK]

Common Mistakes:

• Passing status inside jsonify arguments
• Trying to set status_code attribute directly
• Missing status code tuple on error response