Response object creation in Flask - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ component_behavior

intermediate

What is the output of this Flask response code?

Consider this Flask route code. What will the client receive as the response body?

Flask

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

@app.route('/')
def home():
    return Response('Hello World', status=200, mimetype='text/plain')

A A JSON response with body 'Hello World' and status 200

B A plain text response with body 'Hello World' and status 200

C An HTML response with body 'Hello World' and status 404

D A plain text response with empty body and status 200

💡 Hint

Check the mimetype and status parameters in the Response constructor.

The Response object is created with the string 'Hello World', status 200, and mimetype 'text/plain'. This means the client receives plain text with that exact body and status code.

📝 Syntax

intermediate

Which option correctly creates a JSON response in Flask?

You want to return a JSON response with data {'success': True} and status 201. Which code snippet is correct?

A return Response(json.dumps({'success': True}), status=201, mimetype='application/json')

B return Response(json.dumps({'success': True}), status=201)

C return Response({'success': True}, status=201)

D return Response({'success': True}, status=201, mimetype='application/json')

💡 Hint

Remember that Response expects a string or bytes for the body, not a dict.

Option A correctly converts the dictionary to a JSON string using json.dumps and sets the mimetype to 'application/json'. Option A passes a dict directly causing a TypeError. Option A misses mimetype and passes dict. Option A passes JSON string but misses mimetype, so content type is default.

🔧 Debug

advanced

Why does this Flask response raise a TypeError?

Examine the code below. Why does it raise a TypeError when the route is accessed?

Flask

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

@app.route('/data')
def data():
    return Response({'key': 'value'}, status=200, mimetype='application/json')

A The mimetype 'application/json' is invalid and causes TypeError

B Status code 200 is not allowed with Response and causes TypeError

C Response body must be a string or bytes, not a dict, causing TypeError

D Flask requires jsonify() to create any Response, else TypeError occurs

💡 Hint

Check the type of the first argument passed to Response.

Response expects the body to be a string or bytes. Passing a dict directly causes a TypeError because Flask cannot convert it automatically.

❓ state_output

advanced

What is the status code of this Flask response?

Given this Flask route, what status code will the client receive?

Flask

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

@app.route('/custom')
def custom():
    resp = Response('Done')
    resp.status_code = 202
    return resp

A 202

B 500

C 200

D None

💡 Hint

Look at how the status_code attribute is set before returning the response.

The Response object is created with default status 200, but then status_code is changed to 202 before returning. So the client receives status 202.

🧠 Conceptual

expert

Which statement about Flask Response objects is true?

Select the one true statement about creating Response objects in Flask.

A Setting the status code after returning the Response object changes the response sent to client.

B Response objects can be created with any data type as body; Flask converts it automatically.

C You must always use Flask's jsonify() to create a Response; Response() cannot handle JSON strings.

D Response objects require the body to be bytes or string; passing other types causes errors.

💡 Hint

Think about what types Response accepts for its body parameter.

Flask Response expects the body to be a string or bytes. Passing other types like dict causes errors. jsonify() is a helper but not mandatory. Status code must be set before returning the Response object.

Practice

1. What is the main purpose of a Response object in Flask?

easy

A. To store user session information

B. To send data back to the user's browser

C. To receive data from the user's browser

D. To connect to a database

Solution

1. Step 1: Understand Flask's response role

   A Response object in Flask is what the server sends back to the user's browser after processing a request.

2. Step 2: Identify the correct purpose

   Since the Response object controls what the user receives, it is used to send data back to the browser.

3. Final Answer:

   To send data back to the user's browser -> Option B

4. Quick Check:

   Response object = send data back [OK]

Hint: Response objects send data back to the browser [OK]

Common Mistakes:

• Confusing response with request handling
• Thinking Response stores session data
• Assuming Response connects to databases

2. Which of the following is the correct way to create a Response object with the text 'Hello' and status code 200 in Flask?

easy

A. return Response('Hello', status=200)

B. return Response('Hello', code=200)

C. return Response('Hello', status_code=200)

D. return Response('Hello', stat=200)

Solution

1. Step 1: Recall Response constructor parameters

   The Flask Response object accepts a status parameter to set the HTTP status code.

2. Step 2: Match correct parameter name

   Only status=200 is valid; code, status_code, and stat are invalid.

3. Final Answer:

   return Response('Hello', status=200) -> Option A

4. Quick Check:

   Use status= for HTTP code [OK]

Hint: Use status= to set HTTP status code in Response [OK]

Common Mistakes:

• Using incorrect parameter names like code or stat
• Confusing status with status_code
• Omitting the status parameter

3. What will be the output status code when this Flask code runs?

from flask import Response

resp = Response('Not Found', status=404)
print(resp.status_code)

medium

A. 404

B. 200

C. 500

D. None

Solution

1. Step 1: Check Response creation

   The Response is created with the text 'Not Found' and status=404, which sets the HTTP status code to 404.

2. Step 2: Access status_code attribute

   Printing resp.status_code will output the status code set, which is 404.

3. Final Answer:

   404 -> Option A

4. Quick Check:

   Status code set = printed status_code [OK]

Hint: Response.status_code shows the HTTP status code [OK]

Common Mistakes:

• Assuming default 200 status code
• Confusing status with response content
• Expecting None or error output

4. Identify the error in this Flask code snippet:

from flask import Response

resp = Response('OK', status_code=200)
return resp

medium

A. Response object cannot be returned directly

B. Response content must be bytes, not string

C. Response constructor does not accept status_code parameter

D. Missing import for Flask app

Solution

1. Step 1: Check Response constructor parameters

   The Response object uses status to set HTTP status, not status_code.

2. Step 2: Identify the error

   Using status_code=200 causes a TypeError because it is not a valid parameter.

3. Final Answer:

   Response constructor does not accept status_code parameter -> Option C

4. Quick Check:

   Use status= not status_code in Response [OK]

Hint: Use status=, not status_code= in Response constructor [OK]

Common Mistakes:

• Using status_code instead of status
• Thinking Response content must be bytes
• Assuming Response can't be returned directly

5. You want to create a Flask Response object that returns JSON data {"success": true} with status 201 and a custom header X-Custom: Yes. Which code snippet correctly does this?

hard

A. return Response(json.dumps({"success": true}), status=201, content_type='application/json', headers={'X-Custom': 'Yes'})

B. return Response(json.dumps({"success": true}), status=201, mimetype='application/json', header={'X-Custom': 'Yes'})

C. return Response('{"success": true}', status_code=201, mimetype='application/json', headers={'X-Custom': 'Yes'})

D. return Response('{"success": true}', status=201, mimetype='application/json', headers={'X-Custom': 'Yes'})

Solution

1. Step 1: Check status parameter correctness

   Use status=201 to set the HTTP status code correctly.

2. Step 2: Verify mimetype and headers usage

   mimetype='application/json' correctly sets content type; headers must be a dictionary with correct key.

3. Step 3: Identify errors in other options

   return Response(json.dumps({"success": true}), status=201, content_type='application/json', headers={'X-Custom': 'Yes'}) uses content_type which is valid but misses importing json and json.dumps usage is not shown; return Response('{"success": true}', status_code=201, mimetype='application/json', headers={'X-Custom': 'Yes'}) uses invalid status_code; return Response(json.dumps({"success": true}), status=201, mimetype='application/json', header={'X-Custom': 'Yes'}) uses incorrect header key (should be headers).

4. Final Answer:

   return Response('{"success": true}', status=201, mimetype='application/json', headers={'X-Custom': 'Yes'}) -> Option D

5. Quick Check:

   Status=201, mimetype, headers dict correct [OK]

Hint: Use status=, mimetype=, and headers={} for custom Response [OK]

Common Mistakes:

• Using status_code instead of status
• Wrong headers key name (header vs headers)
• Forgetting to set mimetype for JSON