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.")