login_required decorator in Django - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ component_behavior

intermediate

What happens when an anonymous user accesses a view with @login_required?

Consider a Django view decorated with @login_required. What is the behavior when an anonymous (not logged in) user tries to access this view?

Django

from django.contrib.auth.decorators import login_required
from django.http import HttpResponse

@login_required
def secret_view(request):
    return HttpResponse('Secret content')

A The user sees the 'Secret content' message without logging in.

B The view raises a TypeError because the user is anonymous.

C The user is redirected to the login page defined by LOGIN_URL setting.

D The server returns a 403 Forbidden error.

💡 Hint

Think about what Django does to protect views from anonymous users.

The @login_required decorator checks if the user is authenticated. If not, it redirects them to the login page specified by LOGIN_URL.

📝 Syntax

intermediate

Which code correctly applies @login_required to a class-based view?

You want to protect a Django class-based view using the @login_required decorator. Which option correctly applies it?

Django

from django.contrib.auth.decorators import login_required
from django.utils.decorators import method_decorator
from django.views import View
from django.http import HttpResponse

class MyView(View):
    def get(self, request):
        return HttpResponse('Hello')

A

@method_decorator(login_required, name='dispatch')
class MyView(View):
    def get(self, request):
        return HttpResponse('Hello')

B

@login_required
class MyView(View):
    def get(self, request):
        return HttpResponse('Hello')

C

class MyView(View):
    def get(self, request):
        @login_required
        return HttpResponse('Hello')

D

class MyView(View):
    @login_required
def get(self, request):
        return HttpResponse('Hello')

💡 Hint

Remember that @login_required is a function decorator, and class-based views need a special approach.

For class-based views, you use method_decorator on the dispatch method or with the name argument to apply @login_required properly.

❓ state_output

advanced

What is the value of request.user after @login_required redirects?

In a Django view decorated with @login_required, if the user is not logged in and gets redirected to the login page, what is the value of request.user in the login view?

Django

from django.contrib.auth.decorators import login_required
from django.http import HttpResponse

@login_required
def secret_view(request):
    return HttpResponse(f'User: {request.user}')

A <User: AnonymousUser>

B <User: None>

C Raises AttributeError because user is missing

D <User: admin>

💡 Hint

Think about what Django sets for unauthenticated users.

Django sets request.user to an AnonymousUser instance for users who are not logged in.

🔧 Debug

advanced

Why does @login_required not redirect in this code?

This Django view uses @login_required but anonymous users can still access it. Why?

from django.contrib.auth.decorators import login_required
from django.http import HttpResponse

@login_required
def my_view():
    return HttpResponse('Hello')

A The decorator is applied incorrectly; it should be @login_required() with parentheses.

B The view function is missing the request parameter, so the decorator fails silently.

C LOGIN_URL is not set in settings.py, so redirect does not happen.

D The HttpResponse is returned before the decorator runs.

💡 Hint

Check the function signature carefully.

The view function must accept the request argument. Without it, Django cannot pass the request, so the decorator does not work properly.

🧠 Conceptual

expert

How does @login_required handle the 'next' parameter in redirects?

When @login_required redirects an anonymous user to the login page, it appends a 'next' parameter to the URL. What is the purpose of this 'next' parameter?

A It disables caching on the login page.

B It is used to track how many times the user tried to access protected views.

C It stores the user's session ID for security checks.

D It tells the login view where to redirect the user after successful login.

💡 Hint

Think about user experience after login.

The 'next' parameter holds the original URL the user wanted to visit, so after login, Django can redirect them there.

Practice

1. What is the main purpose of the @login_required decorator in Django?

easy

A. To restrict access to a view only to logged-in users

B. To automatically log out users after a timeout

C. To display a custom error message on login failure

D. To register a new user in the system

Solution

1. Step 1: Understand the role of @login_required

   This decorator is used to protect views so only authenticated users can access them.

2. Step 2: Compare options with the decorator's function

   Only To restrict access to a view only to logged-in users correctly describes restricting access to logged-in users.

3. Final Answer:

   To restrict access to a view only to logged-in users -> Option A

4. Quick Check:

   login_required restricts access = D [OK]

Hint: Remember: login_required means login needed to see page [OK]

Common Mistakes:

• Thinking it logs out users automatically
• Confusing it with user registration
• Assuming it shows error messages

2. Which of the following is the correct way to apply the @login_required decorator to a Django view function named dashboard?

easy

A. def login_required(dashboard):

B. @login_required\ndef dashboard(request):

C. dashboard = login_required(dashboard(request))

D. login_required @dashboard(request):

Solution

1. Step 1: Recall the syntax for decorators in Python

   Decorators are placed above the function with an @ symbol, like @login_required.

2. Step 2: Check which option uses this syntax correctly

   @login_required\ndef dashboard(request): correctly places @login_required above the function definition.

3. Final Answer:

   @login_required\ndef dashboard(request): -> Option B

4. Quick Check:

   Decorator syntax uses @ above function = A [OK]

Hint: Decorator always goes above function with @ [OK]

Common Mistakes:

• Trying to call decorator like a function without @
• Placing decorator after function definition
• Using invalid syntax like 'login_required @dashboard'

3. Given this Django view code snippet, what happens when an anonymous user tries to access /profile/?

@login_required
def profile(request):
    return HttpResponse('User Profile')

medium

A. The user is redirected to the login page

B. The user gets a 404 Not Found error

C. The user sees 'User Profile' page

D. The user sees a permission denied message

Solution

1. Step 1: Understand what @login_required does for anonymous users

   It redirects users who are not logged in to the login page.

2. Step 2: Match this behavior with the options

   The user is redirected to the login page correctly states the redirect to login page for anonymous users.

3. Final Answer:

   The user is redirected to the login page -> Option A

4. Quick Check:

   Anonymous user triggers redirect = C [OK]

Hint: Anonymous users get redirected, not error or content [OK]

Common Mistakes:

• Assuming anonymous users see the page content
• Thinking it returns 404 error
• Believing it shows permission denied instead of redirect

4. Identify the error in this Django view using @login_required:

from django.contrib.auth.decorators import login_required
from django.http import HttpResponse

@login_required()
def dashboard(request):
    return HttpResponse('Dashboard')

medium

A. Missing import for HttpResponse

B. Missing request parameter in function

C. Function name should be capitalized

D. Incorrect use of parentheses after @login_required

Solution

1. Step 1: Check the decorator usage syntax

   @login_required is used without parentheses unless passing arguments.

2. Step 2: Identify the incorrect parentheses usage

   Incorrect use of parentheses after @login_required points out the error of using @login_required() instead of @login_required.

3. Final Answer:

   Incorrect use of parentheses after @login_required -> Option D

4. Quick Check:

   Decorator without args has no () = B [OK]

Hint: Use @login_required without () unless arguments needed [OK]

Common Mistakes:

• Adding parentheses when not required
• Forgetting to import HttpResponse (not tested here)
• Changing function name case unnecessarily

5. You want to protect a class-based view DashboardView so only logged-in users can access it. Which is the correct way to apply login_required?

hard

A. Call login_required inside the dispatch method manually

B. Add @login_required above the class definition

C. Use LoginRequiredMixin as a parent class instead of login_required

D. Wrap the class with login_required(DashboardView) after defining it

Solution

1. Step 1: Recall how to protect class-based views in Django

   For class-based views, Django provides LoginRequiredMixin to enforce login.

2. Step 2: Evaluate the options for class-based view protection

   Use LoginRequiredMixin as a parent class instead of login_required correctly uses LoginRequiredMixin as a parent class, which is the standard pattern.

3. Final Answer:

   Use LoginRequiredMixin as a parent class instead of login_required -> Option C

4. Quick Check:

   Class views use mixins, not decorators = A [OK]

Hint: Use LoginRequiredMixin for class views, not @login_required [OK]

Common Mistakes:

• Trying to decorate class directly with @login_required
• Wrapping class after definition with login_required
• Manually calling login_required inside methods