Login view and template in Django - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ component_behavior

intermediate

What does this Django login view render on GET request?

Consider this Django view code for login. What template does it render when accessed with a GET request?

Django

from django.shortcuts import render, redirect
from django.contrib.auth import authenticate, login

def login_view(request):
    if request.method == 'POST':
        username = request.POST.get('username')
        password = request.POST.get('password')
        user = authenticate(request, username=username, password=password)
        if user is not None:
            login(request, user)
            return redirect('home')
        else:
            return render(request, 'login.html', {'error': 'Invalid credentials'})
    else:
        return render(request, 'login.html')

A Redirects to 'home' on GET request

B Renders 'login.html' template without any context on GET

C Renders 'home.html' template on GET

D Raises a 404 error on GET request

💡 Hint

Check what happens when the request method is not POST.

The view checks if the request method is POST to process login. For GET requests, it renders 'login.html' without extra context.

📝 Syntax

intermediate

Which option correctly includes CSRF token in Django login template?

In Django templates, to protect POST forms from CSRF attacks, which snippet correctly includes the CSRF token inside the form?

Django

<form method="post" action="">
    <!-- CSRF token here -->
    <input type="text" name="username" />
    <input type="password" name="password" />
    <button type="submit">Login</button>
</form>

A {% csrf_token %}

B {{ csrf_token }}

C <input type="hidden" name="csrfmiddlewaretoken" value="{{ csrf_token }}">

D <csrf_token />

💡 Hint

Django uses a special template tag for CSRF tokens.

Django requires the template tag {% csrf_token %} inside POST forms to add the CSRF token input automatically.

❓ state_output

advanced

What is the value of 'error' in context after failed login POST?

Given this login view, what will be the value of 'error' in the context passed to the template after a failed login attempt?

Django

def login_view(request):
    if request.method == 'POST':
        username = request.POST.get('username')
        password = request.POST.get('password')
        user = authenticate(request, username=username, password=password)
        if user is not None:
            login(request, user)
            return redirect('home')
        else:
            return render(request, 'login.html', {'error': 'Invalid credentials'})
    else:
        return render(request, 'login.html')

A 'Invalid credentials'

B KeyError because 'error' is missing

C Empty string ''

D None

💡 Hint

Look at the else block inside the POST method.

When authentication fails, the view renders 'login.html' with context {'error': 'Invalid credentials'}.

🔧 Debug

advanced

Why does this login view raise a TypeError?

Identify the cause of the TypeError in this Django login view snippet.

Django

def login_view(request):
    if request.method == 'POST':
        username = request.POST['username']
        password = request.POST['password']
        user = authenticate(username=username, password=password)
        if user:
            login(request, user)
            return redirect('home')
        else:
            return render(request, 'login.html', {'error': 'Invalid credentials'})
    return render(request, 'login.html')

A redirect called without parentheses

B login function called with wrong number of arguments

C authenticate missing 'request' argument causes TypeError

D request.POST['username'] raises KeyError

💡 Hint

Check the signature of authenticate in Django 4+.

In Django 4+, authenticate requires the request argument. Omitting it causes a TypeError.

🧠 Conceptual

expert

Which option best describes the purpose of 'login' function in Django views?

In Django, what is the main effect of calling the 'login(request, user)' function inside a view?

A It logs the user out and clears the session

B It creates a new user account in the database

C It redirects the user to the login page

D It sets the user ID in the session to mark the user as authenticated

💡 Hint

Think about what happens after a successful login.

The login function saves the user's ID in the session so Django knows the user is authenticated on future requests.

Practice

1. What is the main purpose of Django's LoginView?

easy

A. To display a list of logged-in users

B. To create a new user registration form

C. To handle password reset requests

D. To provide a ready-made view for user login handling

Solution

1. Step 1: Understand Django's built-in views

   Django provides LoginView as a built-in class-based view to handle user login functionality easily.

2. Step 2: Identify the purpose of LoginView

   It manages displaying the login form, validating user credentials, and logging users in.

3. Final Answer:

   To provide a ready-made view for user login handling -> Option D

4. Quick Check:

   LoginView = ready-made login handler [OK]

Hint: LoginView is for login pages, not registration or reset [OK]

Common Mistakes:

• Confusing LoginView with registration or password reset views
• Thinking LoginView lists users
• Assuming LoginView creates new users

2. Which of the following is the correct way to specify a custom template for Django's LoginView?

easy

A. template = 'login.html'

B. template_name = 'login.html'

C. templateFile = 'login.html'

D. templatePath = 'login.html'

Solution

1. Step 1: Recall Django's class-based view attribute for templates

   Django's class-based views use the attribute template_name to specify the HTML template file.

2. Step 2: Match the correct attribute name

   Among the options, only template_name is the correct attribute to set the template.

3. Final Answer:

   template_name = 'login.html' -> Option B

4. Quick Check:

   Use template_name to set template in CBVs [OK]

Hint: Remember: class-based views use template_name, not template [OK]

Common Mistakes:

• Using 'template' instead of 'template_name'
• Using camelCase like 'templateFile' or 'templatePath'
• Forgetting to set template_name at all

3. Given this simple login template snippet:

<form method="post">
  {% csrf_token %}
  {{ form.as_p }}
  <button type="submit">Login</button>
</form>

What will happen if the {% csrf_token %} tag is removed?

medium

A. The form will submit successfully without any issues

B. The form will submit but the user will not be logged in

C. Django will raise a CSRF verification failed error on form submission

D. The form will redirect to the homepage automatically

Solution

1. Step 1: Understand CSRF protection in Django forms

   Django requires a CSRF token in POST forms to protect against cross-site request forgery attacks.

2. Step 2: Effect of removing the CSRF token

   If the {% csrf_token %} tag is missing, Django will reject the POST request with a CSRF verification error.

3. Final Answer:

   Django will raise a CSRF verification failed error on form submission -> Option C

4. Quick Check:

   Missing csrf_token causes CSRF error [OK]

Hint: Always include {% csrf_token %} in POST forms [OK]

Common Mistakes:

• Assuming form submits without CSRF token
• Thinking user won't log in but no error occurs
• Believing form redirects automatically without token

4. You wrote this URL pattern for login:

path('login/', LoginView.as_view(template_name='login.html'))

But when you visit /login/, you get a TemplateDoesNotExist error. What is the most likely cause?

medium

A. The template file 'login.html' is missing or not in the correct templates directory

B. You forgot to import LoginView from django.contrib.auth.views

C. You need to add a trailing slash in the URL pattern

D. The URL pattern should be named 'login_view' instead of 'login/'

Solution

1. Step 1: Understand TemplateDoesNotExist error

   This error means Django cannot find the specified template file in any of the configured template directories.

2. Step 2: Check common causes

   Since the URL pattern and import are likely correct, the most common cause is the missing or misplaced template file.

3. Final Answer:

   The template file 'login.html' is missing or not in the correct templates directory -> Option A

4. Quick Check:

   TemplateDoesNotExist = missing or misplaced template [OK]

Hint: Check template file location if TemplateDoesNotExist error appears [OK]

Common Mistakes:

• Assuming import errors cause TemplateDoesNotExist
• Thinking URL pattern naming affects template loading
• Ignoring template directory settings

5. You want to customize the login form to add a 'Remember Me' checkbox that keeps users logged in longer. Which approach correctly integrates this feature using Django's LoginView?

hard

A. Override LoginView to add a custom form with a 'remember_me' field and adjust session expiry in form_valid

B. Add a checkbox in the template only; Django handles session duration automatically

C. Set template_name to a new template with the checkbox but do not change the view or form

D. Use Django's default LoginView without changes; 'Remember Me' is built-in

Solution

1. Step 1: Understand customizing LoginView

   To add new fields like 'Remember Me', you must create a custom form and override LoginView to use it.

2. Step 2: Adjust session expiry based on 'remember_me'

   Override form_valid method to set session expiry longer if 'remember_me' is checked.

3. Final Answer:

   Override LoginView to add a custom form with a 'remember_me' field and adjust session expiry in form_valid -> Option A

4. Quick Check:

   Custom form + override form_valid for 'Remember Me' [OK]

Hint: Customize form and override form_valid to handle 'Remember Me' [OK]

Common Mistakes:

• Adding checkbox only in template without backend logic
• Assuming default LoginView supports 'Remember Me' automatically
• Not overriding form_valid to change session expiry