Setting and reading cookies in Flask - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to set a cookie named 'username' with value 'Alice'.

Flask

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

@app.route('/')
def index():
    resp = make_response('Setting cookie')
    resp.set_cookie('[1]', 'Alice')
    return resp

Drag options to blanks, or click blank then click option'

Aname

Buser

Cusername

Duser_id

Attempts:

3 left

💡 Hint

Common Mistakes

Using a wrong cookie name like 'user' or 'name' instead of 'username'.

Forgetting to call set_cookie on the response object.

The cookie name is 'username', so you must pass 'username' as the first argument to set_cookie.

2fill in blank

medium

Complete the code to read the cookie named 'username' from the request.

Flask

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

@app.route('/get')
def get_cookie():
    user = request.cookies.get('[1]')
    return f'User is {user}'

Drag options to blanks, or click blank then click option'

Auser

Busername

Cname

Dsession

Attempts:

3 left

💡 Hint

Common Mistakes

Using a wrong cookie name like 'user' or 'session'.

Trying to access cookies directly without using request.cookies.get().

To read the cookie named 'username', use request.cookies.get('username').

3fill in blank

hard

Fix the error in the code to set a cookie with expiration of 1 day.

Flask

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

@app.route('/set')
def set_cookie():
    resp = make_response('Cookie set')
    resp.set_cookie('token', 'abc123', max_age=[1])
    return resp

Drag options to blanks, or click blank then click option'

A86400

Btimedelta(days=1)

C24*60*60*1000

DNone

Attempts:

3 left

💡 Hint

Common Mistakes

Passing a timedelta object instead of seconds.

Using milliseconds instead of seconds.

Passing None which disables expiration.

The max_age parameter expects seconds as an integer. 1 day = 86400 seconds.

4fill in blank

hard

Fill both blanks to set a cookie named 'sessionid' with value 'xyz' that expires in 2 hours.

Flask

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

@app.route('/session')
def session_cookie():
    resp = make_response('Session cookie set')
    resp.set_cookie('[1]', '[2]', max_age=7200)
    return resp

Drag options to blanks, or click blank then click option'

Asessionid

Buserid

Cxyz

Dabc

Attempts:

3 left

💡 Hint

Common Mistakes

Swapping cookie name and value.

Using wrong cookie names or values.

The cookie name is 'sessionid' and the value is 'xyz'. The max_age is 7200 seconds (2 hours).

5fill in blank

hard

Fill all three blanks to read a cookie named 'auth' and return 'Logged in' if it exists, else 'Not logged in'.

Flask

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

@app.route('/auth')
def check_auth():
    token = request.cookies.get('[1]')
    if token [2] None:
        return '[3]'
    else:
        return 'Not logged in'

Drag options to blanks, or click blank then click option'

Aauth

B!=

CLogged in

D==

Attempts:

3 left

💡 Hint

Common Mistakes

Using wrong cookie name.

Using wrong comparison operator.

Returning wrong strings.

We get the cookie named 'auth'. If it is not None, return 'Logged in'. Otherwise, return 'Not logged in'.

Practice

1. What is the main purpose of using cookies in a Flask web application?

easy

A. To increase the speed of the Flask server

B. To run server-side scripts automatically

C. To change the HTML structure of a webpage

D. To store small pieces of data on the user's browser for later use

Solution

1. Step 1: Understand what cookies do

   Cookies store small data on the user's browser to remember information like login status or preferences.

2. Step 2: Identify the correct purpose in Flask context

   Flask uses cookies to save data on the client side, not to run server scripts or change server speed.

3. Final Answer:

   To store small pieces of data on the user's browser for later use -> Option D

4. Quick Check:

   Cookies save data on browser = C [OK]

Hint: Cookies save data on browser, not server tasks [OK]

Common Mistakes:

• Thinking cookies run server scripts
• Confusing cookies with server speed optimization
• Believing cookies change webpage HTML structure

2. Which of the following is the correct way to set a cookie named user_id with value 123 in Flask?

easy

A. response.cookies.set('user_id', 123)

B. response.set_cookie('user_id', '123')

C. request.set_cookie('user_id', '123')

D. request.cookies.set('user_id', '123')

Solution

1. Step 1: Identify the correct method to set cookies

   Cookies are set on the response object using set_cookie method.

2. Step 2: Check the value type and object used

   The value must be a string, so '123' is correct. Also, setting cookies on request object is invalid.

3. Final Answer:

   response.set_cookie('user_id', '123') -> Option B

4. Quick Check:

   Use response.set_cookie with string value = A [OK]

Hint: Use response.set_cookie with string values [OK]

Common Mistakes:

• Using request object to set cookies
• Passing integer instead of string as cookie value
• Calling set_cookie on request.cookies

3. Given this Flask route code, what will be the output when accessing /get_cookie after setting the cookie username to alice?

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

@app.route('/set_cookie')
def set_cookie():
    resp = make_response('Cookie Set')
    resp.set_cookie('username', 'alice')
    return resp

@app.route('/get_cookie')
def get_cookie():
    user = request.cookies.get('username')
    return f'User: {user}'

medium

A. User: alice

B. User: None

C. User: username

D. Error: Cookie not found

Solution

1. Step 1: Understand cookie setting route

   The /set_cookie route sets a cookie named 'username' with value 'alice' on the response.

2. Step 2: Understand cookie reading route

   The /get_cookie route reads the 'username' cookie from the request and returns it in the string.

3. Final Answer:

   User: alice -> Option A

4. Quick Check:

   Cookie 'username' = 'alice' read correctly = A [OK]

Hint: Set cookie first, then read with request.cookies.get() [OK]

Common Mistakes:

• Expecting cookie value before setting it
• Confusing cookie name with value
• Assuming error if cookie missing without checking

4. Identify the error in this Flask code snippet that tries to read a cookie named session_id:

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

@app.route('/check')
def check():
    session = request.cookies['session_id']
    return f'Session: {session}'

medium

A. Should use response.cookies instead of request.cookies

B. Cookie name must be capitalized as 'Session_id'

C. Using square brackets to access cookie may cause KeyError if cookie missing

D. Flask does not support reading cookies

Solution

1. Step 1: Check how cookie is accessed

   The code uses request.cookies['session_id'] which raises KeyError if cookie is missing.

2. Step 2: Suggest safer method

   Using request.cookies.get('session_id') returns None if cookie missing, avoiding error.

3. Final Answer:

   Using square brackets to access cookie may cause KeyError if cookie missing -> Option C

4. Quick Check:

   Access cookie safely with get() to avoid errors = B [OK]

Hint: Use request.cookies.get() to avoid KeyError [OK]

Common Mistakes:

• Using response.cookies to read cookies
• Assuming cookie names are case-insensitive
• Ignoring possibility of missing cookies causing errors

5. You want to create a Flask route that sets a cookie named theme with value dark that expires in 7 days. Which code snippet correctly does this?

hard

A. resp.set_cookie('theme', 'dark', max_age=7*24*60*60)

B. resp.set_cookie('theme', 'dark', expires=7)

C. resp.set_cookie('theme', 'dark', max_age=7)

D. resp.set_cookie('theme', 'dark', expires='7 days')

Solution

1. Step 1: Understand cookie expiration parameters

   To set expiration, use max_age in seconds or expires as a datetime object.

2. Step 2: Calculate 7 days in seconds and check syntax

   7 days = 7*24*60*60 seconds. resp.set_cookie('theme', 'dark', max_age=7*24*60*60) uses max_age correctly with this calculation.

3. Final Answer:

   resp.set_cookie('theme', 'dark', max_age=7*24*60*60) -> Option A

4. Quick Check:

   Use max_age in seconds for 7 days = D [OK]

Hint: Use max_age in seconds for cookie expiry [OK]

Common Mistakes:

• Passing expires as integer days instead of seconds or datetime
• Using string '7 days' which is invalid
• Confusing max_age and expires parameters