Response headers in Flask - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ component_behavior

intermediate

What is the output of this Flask response header code?

Consider this Flask route that sets a custom response header. What will the client receive in the response headers?

Flask

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

@app.route('/')
def index():
    response = make_response('Hello World')
    response.headers['X-Custom-Header'] = 'MyValue'
    return response

A The response includes a header 'X-Custom-Header' with value 'Hello World'.

B The response includes a header 'X-Custom-Header' with value 'MyValue'.

C The response has no custom headers; only default headers are sent.

D The code raises a runtime error because headers cannot be set this way.

💡 Hint

Think about how Flask's make_response allows modifying headers before sending.

Using make_response, you can add or modify headers before returning the response. Here, 'X-Custom-Header' is set to 'MyValue', so the client receives it.

📝 Syntax

intermediate

Which option correctly sets multiple headers in a Flask response?

You want to set two headers: 'Cache-Control' to 'no-cache' and 'X-Powered-By' to 'Flask'. Which code snippet does this correctly?

Flask

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

@app.route('/')
def index():
    response = make_response('Hello')
    # Set headers here
    return response

A

response.headers['Cache-Control'] = 'no-cache'
response.headers['X-Powered-By'] = 'Flask'

B

response.headers.add('Cache-Control', 'no-cache')
response.headers.add('X-Powered-By', 'Flask')

C response.headers = {'Cache-Control': 'no-cache', 'X-Powered-By': 'Flask'}

D

response.set_header('Cache-Control', 'no-cache')
response.set_header('X-Powered-By', 'Flask')

💡 Hint

Headers behave like a dictionary in Flask response objects.

The headers attribute is a dictionary-like object. You can assign values by key. Option A replaces the entire headers object which is not allowed. Option A and D use non-existent methods.

🔧 Debug

advanced

Why does this Flask code fail to send the custom header?

Look at this Flask route. Why does the client not receive the 'X-Test' header?

Flask

from flask import Flask
app = Flask(__name__)

@app.route('/')
def index():
    response = 'Hello'
    response.headers['X-Test'] = '123'
    return response

A Because the header name 'X-Test' is reserved and ignored by Flask.

B Because Flask automatically strips custom headers unless explicitly allowed.

C Because headers must be set before returning the string, using a decorator.

D Because 'response' is a string, not a response object, so it has no headers attribute.

💡 Hint

Check the type of the response variable before setting headers.

The variable 'response' is a plain string. Strings do not have a headers attribute. You must create a response object (e.g., with make_response) to set headers.

❓ state_output

advanced

What is the value of the 'Content-Type' header after this Flask route runs?

Given this Flask route, what will be the 'Content-Type' header in the response?

Flask

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

@app.route('/')
def index():
    response = make_response('<h1>Hi</h1>')
    response.headers['Content-Type'] = 'application/json'
    return response

A 'application/json'

B 'text/html; charset=utf-8'

C 'text/plain'

D No 'Content-Type' header is set

💡 Hint

Headers set explicitly override defaults.

The code explicitly sets 'Content-Type' to 'application/json', so this header value is sent to the client.

🧠 Conceptual

expert

Which statement about Flask response headers is true?

Choose the correct statement about how Flask handles response headers.

A Headers set on the response object are ignored if the response body is a string.

B Flask automatically merges duplicate headers with the same name into a single header.

C Flask response headers can be modified only before the response is returned, not after.

D Flask requires headers to be set using a special decorator, not directly on the response.

💡 Hint

Think about when the response is finalized and sent.

Headers must be set before returning the response object. After returning, the response is sent and headers cannot be changed. Other options are incorrect because Flask does not merge duplicate headers automatically, headers are respected regardless of body type if response object is used, and no special decorator is needed.