404_templates.md

Adventures in Django: Customizing 404 templates

There are many HTTP status codes that can be returned from a web server; one of them is the infamous 404 Not found error code. This error is raised when a particular page cannot be located on the website. Django handles the Http404 exception by displaying a default error page for our application.

If we set the option DEBUG=True in our project's settings.py file, we will see something like this.

Otherwise, if we set DEBUG=False, we will see this instead.

We typically disable debugging in a production site and Django provides a standard 404 page like the one above for us. The good news is we can replace the default 404 page with a custom template. Django requires that we name this template 404.html and that we place it in the root template directory. This is the templates subdirectory residing in the inner project directory.

myproject
   |--myapp
   |----migrations
   |--myproject
   |----__pycache__
   |----templates     <==

We also need to make sure the DIRS key in the TEMPLATES variable in our project's settings.py file is not an empty list.

TEMPLATES = [
    {
        'BACKEND': 'django.template.backends.django.DjangoTemplates',
        'DIRS': [str(BASE_DIR.joinpath('myproject/templates'))],              # <==
        'APP_DIRS': True,
        'OPTIONS': {
            'context_processors': [
                'django.template.context_processors.debug',
                'django.template.context_processors.request',
                'django.contrib.auth.context_processors.auth',
                'django.contrib.messages.context_processors.messages',
            ],
        },
    },
]

Notice in the above example that the DIRS key is assigned a concatenated string of the BASE_DIR value and myproject/templates. The BASE_DIR is the directory path that contains manage.py. After restarting our Django server and entering an invalid url on our browser, we will see our custom 404 page displayed.

If Django cannot locate the 404.html template in the root template directory, then Django will look for it in the app's templates directory if APP_DIRS is set to True.

myproject
   |--myapp
   |----__pycache__
   |----migrations
   |------__pycache__
   |----templates        <==
   |------planner
   |--myproject
   |----__pycache__
   |----templates     

Having two instances of 404.html residing in two different templates directories (root and app) such as this:

$ find . -name 404.html
./myproject/myapp/templates/404.html
./myproject/myproject/templates/404.html

may be helpful but we have to configure our project's settings.py file to let Django know which instance we prefer. If we want the app's 404.html to take over, then we need to reset the DIRS key back to an empty list, [].

TEMPLATES = [
    {
        'BACKEND': 'django.template.backends.django.DjangoTemplates',
        'DIRS': [],              # <==
        'APP_DIRS': True,
        'OPTIONS': {
            'context_processors': [
                'django.template.context_processors.debug',
                'django.template.context_processors.request',
                'django.contrib.auth.context_processors.auth',
                'django.contrib.messages.context_processors.messages',
            ],
        },
    },
]

Conclusion

Django makes it rather straightforward to customize error pages besides 404.html. We can also provide custom 400.html, 403.html and 500.html pages for HTTP Bad Request, Forbidden and Internal Server Error error codes respectively. Thank you for reading and Happy Django!