Django Exceptions

In Django, an exception is an error that occurs during the execution of your application. Exceptions disrupt the normal flow of a program and can be caused by various issues such as invalid user input, database errors, or bugs in the code.

How Django Handles Exceptions

Django has a robust exception-handling system that:

1. Detects exceptions during the request/response cycle.

2. Provides error messages to developers (detailed error pages in debug mode).

3. Returns appropriate HTTP responses to users in production mode.

Common Types of Django Exceptions

There are some common exceptions

1. Http404

Raised when a requested resource (like a page or object) is not found.

Example:


from django.http import Http404

def my_view(request):
    if not some_condition:
        raise Http404("Page not found")

2. PermissionDenied

It is raised when a user doesn’t have permission to access a view or resource.

Example


from django.core.exceptions import PermissionDenied

def my_view(request):
    if not request.user.is_staff:
        raise PermissionDenied("You do not have permission to view this page.")

3. ValidationError

Raised when data doesn’t pass validation rules.

Example:


from django.core.exceptions import ValidationError

def validate_positive(value):
    if value < 0:
        raise ValidationError(f"{value} is not a positive number.")

4. ObjectDoesNotExist

Raised when a database query doesn’t find a matching object.

Example:


from django.shortcuts import get_object_or_404
from myapp.models import MyModel

def my_view(request, id):
    obj = get_object_or_404(MyModel, id=id)
    return obj

5. SuspiciousOperation

Raised when the framework detects potentially malicious activity (e.g., invalid input, tampered cookies).

Example:


from django.core.exceptions import SuspiciousOperation

def my_view(request):
    if "bad_input" in request.GET:
        raise SuspiciousOperation("Invalid request.")