Setting and getting session data in Django - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is a session in Django?

A session in Django is a way to store data on the server side for a particular user across multiple requests. It helps keep user-specific information like login status or preferences.

beginner

How do you set a session variable in a Django view?

You set a session variable by assigning a value to a key in the request.session dictionary, like request.session['key'] = value.

beginner

How do you retrieve a session variable safely in Django?

Use request.session.get('key') to get the value. It returns None if the key does not exist, avoiding errors.

intermediate

What happens if you try to access a session key that does not exist using request.session['key']?

Django raises a KeyError because the key is missing. To avoid this, use request.session.get('key').

intermediate

How can you delete a session variable in Django?

Use del request.session['key'] to remove a session variable. This deletes the key and its value from the session data.

Which of these is the correct way to set a session variable in Django?

A request.session['user'] = 'Alice'

B request.set_session('user', 'Alice')

C session['user'] = 'Alice'

D request.session.set('user', 'Alice')

In Django, session data is set by assigning a value to a key in request.session like a dictionary.

How do you safely get a session value that might not exist?

A request.session.get('key')

B request.session['key']

C request.get_session('key')

D request.session.fetch('key')

Using request.session.get('key') returns None if the key is missing, preventing errors.

What error occurs if you access a missing session key with request.session['key']?

A ValueError

B AttributeError

C TypeError

D KeyError

Accessing a missing key in a dictionary-like object raises a KeyError.

How do you delete a session variable named 'cart'?

A request.session.remove('cart')

B del request.session['cart']

C request.session['cart'] = None

D request.session.pop('cart')

Deleting a session key is done with del request.session['cart'].

Where is session data stored in Django by default?

A In server-side files

B In browser cookies

C In the database

D In local storage

By default, Django stores session data in the database, keeping it secure on the server.

Explain how to set, get, and delete session data in a Django view.

Think of request.session as a dictionary to store user data.

Describe what happens if you try to access a session key that does not exist using request.session['key'] and how to avoid errors.

Consider how dictionary access works in Python.

Practice

1. What is the correct way to store a user's favorite color in Django session inside a view?

easy

A. request.session['favorite_color'] = 'blue'

B. request.session.set('favorite_color', 'blue')

C. session['favorite_color'] = 'blue'

D. request.set_session('favorite_color', 'blue')

Solution

1. Step 1: Understand Django session assignment

   In Django, session data is stored by assigning a value to a key in request.session like a dictionary.

2. Step 2: Identify correct syntax for setting session data

   The correct syntax is request.session['key'] = value. Methods like set or set_session do not exist.

3. Final Answer:

   request.session['favorite_color'] = 'blue' -> Option A

4. Quick Check:

   Set session data with dictionary syntax [OK]

Hint: Use dictionary style assignment to set session data [OK]

Common Mistakes:

• Using non-existent methods like set() or set_session()
• Trying to assign session data without request.session
• Using session variable without request object

2. Which of the following is the correct syntax to retrieve a session value safely with a default in Django?

easy

A. request.session.get('user_id' : None)

B. request.session['user_id', None]

C. request.session.fetch('user_id', None)

D. request.session.get('user_id', None)

Solution

1. Step 1: Recall the method to get session data safely

   Django sessions use the dictionary method get(key, default) to retrieve values safely without error if key is missing.

2. Step 2: Identify correct syntax

   The correct syntax is request.session.get('user_id', None). Using brackets with comma or colon is invalid syntax, and fetch is not a valid method.

3. Final Answer:

   request.session.get('user_id', None) -> Option D

4. Quick Check:

   Use get() with key and default [OK]

Hint: Use get() method with key and default to avoid errors [OK]

Common Mistakes:

• Using brackets with comma or colon inside session access
• Using non-existent fetch() method
• Accessing session key directly without default causing KeyError

3. Given the following Django view code snippet, what will be the output if the session has no 'visits' key initially?

def my_view(request):
    visits = request.session.get('visits', 0)
    visits += 1
    request.session['visits'] = visits
    return HttpResponse(f"Visit count: {visits}")

medium

A. Visit count: None

B. Visit count: 0

C. Visit count: 1

D. KeyError exception

Solution

1. Step 1: Understand default value usage in get()

   The code uses request.session.get('visits', 0) which returns 0 if 'visits' key is missing.

2. Step 2: Follow the increment and assignment

   It adds 1 to visits (0 + 1 = 1), then stores it back in session and returns the string with visits value.

3. Final Answer:

   Visit count: 1 -> Option C

4. Quick Check:

   Default 0 + 1 increment = 1 [OK]

Hint: Default value in get() prevents KeyError, then increment [OK]

Common Mistakes:

• Assuming visits starts at None or causes error
• Forgetting to add 1 before storing
• Expecting KeyError when key is missing

4. Identify the error in this Django view code that tries to get a session value:

def view(request):
    user = request.session['user', 'guest']
    return HttpResponse(user)

medium

A. TypeError because session is not subscriptable

B. KeyError if 'user' key missing

C. Returns 'guest' string correctly

D. SyntaxError due to incorrect session key access

Solution

1. Step 1: Analyze session key access syntax

   The code uses request.session['user', 'guest'] which passes a tuple ('user', 'guest') as the key.

2. Step 2: Identify correct way to provide default

   This raises KeyError if the tuple key is missing. To get 'user' with default 'guest', use request.session.get('user', 'guest').

3. Final Answer:

   KeyError if 'user' key missing -> Option B

4. Quick Check:

   Tuple in brackets causes KeyError [OK]

Hint: Use get() for default, not tuple keys in brackets [OK]

Common Mistakes:

• Using tuple inside brackets for session key
• Expecting bracket syntax to accept default value
• Confusing dictionary get() method with bracket access

5. You want to track a user's last visited page URL in session and display it on the next page visit. Which code snippet correctly sets and gets this session data in Django?

hard

A. last = request.session.get('last_page', 'None'); request.session['last_page'] = request.path

B. request.session['last_page'] = request.path; last = request.session.get('last_page', 'None')

C. request.session.set('last_page', request.path); last = request.session['last_page']

D. last = request.session['last_page']; request.session['last_page'] = request.path

Solution

1. Step 1: Understand the order of getting and setting session data

   To show the last visited page, first get the stored value, then update it with the current page path.

2. Step 2: Identify correct code order and methods

   last = request.session.get('last_page', 'None'); request.session['last_page'] = request.path first retrieves last_page with a default, then updates it with request.path. Other options set before getting or use invalid methods.

3. Final Answer:

   last = request.session.get('last_page', 'None'); request.session['last_page'] = request.path -> Option A

4. Quick Check:

   Get old value before updating session [OK]

Hint: Get session value before updating it to show previous data [OK]

Common Mistakes:

• Setting session before getting old value loses previous data
• Using non-existent set() method
• Accessing session key directly without default causing error