Creating custom middleware in Django - Practice Exercises

Challenge - 5 Problems

❓ component_behavior

intermediate

What is the output of this custom middleware modifying response headers?

Consider this Django middleware that adds a custom header to every response. What will be the value of the X-Custom-Header in the HTTP response?

Django

class CustomHeaderMiddleware:
    def __init__(self, get_response):
        self.get_response = get_response

    def __call__(self, request):
        response = self.get_response(request)
        response["X-Custom-Header"] = "MiddlewareActive"
        return response

A "MiddlewareActive"

B Header will not be present

C "CustomHeader"

D Raises AttributeError

💡 Hint

Think about how the middleware modifies the response object before returning it.

The middleware adds the header X-Custom-Header with value MiddlewareActive to every response before returning it.

❓ lifecycle

intermediate

At which point in the request lifecycle is the process_view middleware method called?

In Django middleware, when is the process_view method executed?

A After the response is returned

B Before the view function is called, after URL resolution

C Before URL resolution

D After the view function is called

💡 Hint

Think about when Django knows which view will handle the request.

process_view runs after Django resolves the URL to a view but before the view function is executed.

📝 Syntax

advanced

Which middleware class definition correctly implements __init__ and __call__ methods?

Select the option that correctly defines a Django middleware class with proper __init__ and __call__ methods.

A

class MyMiddleware:
    def __init__(self, get_response):
        self.get_response = get_response
    def __call__(self):
        response = self.get_response()
        return response

B

class MyMiddleware:
    def __call__(self, get_response):
        self.get_response = get_response
    def __init__(self, request):
        response = self.get_response(request)
        return response

C

class MyMiddleware:
    def __init__(self):
        pass
    def __call__(self, request, get_response):
        response = get_response(request)
        return response

D

class MyMiddleware:
    def __init__(self, get_response):
        self.get_response = get_response
    def __call__(self, request):
        response = self.get_response(request)
        return response

💡 Hint

Remember the middleware class must accept get_response in __init__ and request in __call__.

Option D correctly defines __init__ with get_response and __call__ with request, calling get_response(request). Others have wrong method signatures.

🔧 Debug

advanced

Why does this middleware raise an AttributeError?

Given this middleware code, why does it raise an AttributeError when processing a request?

Django

class FaultyMiddleware:
    def __init__(self, get_response):
        pass

    def __call__(self, request):
        response = self.get_response(request)
        return response

A Because __init__ should not accept get_response parameter

B Because __call__ method is missing the request parameter

C Because self.get_response is not assigned in __init__, so calling it raises AttributeError

D Because the middleware must return a string, not a response object

💡 Hint

Check if all attributes used in __call__ are properly set in __init__.

The middleware does not assign get_response to self.get_response in __init__, so self.get_response is undefined in __call__, causing AttributeError.

❓ state_output

expert

What is the final value of request.custom_flag after this middleware stack runs?

Two middlewares modify request.custom_flag. What is its value after both run?

Django

class MiddlewareOne:
    def __init__(self, get_response):
        self.get_response = get_response
    def __call__(self, request):
        request.custom_flag = True
        response = self.get_response(request)
        return response

class MiddlewareTwo:
    def __init__(self, get_response):
        self.get_response = get_response
    def __call__(self, request):
        if hasattr(request, 'custom_flag') and request.custom_flag:
            request.custom_flag = False
        response = self.get_response(request)
        return response

# Assume MiddlewareOne is listed before MiddlewareTwo in MIDDLEWARE setting

A False

B True

C AttributeError because custom_flag is missing

D None

💡 Hint

Remember middleware runs in order on request, reverse order on response.

MiddlewareOne sets custom_flag to True first. MiddlewareTwo then sees it True and sets it to False. So final value after both is False.