This is a small definition of custom error 404 page (Not found) on a Django view... With this kind of definition we're using a http class to generate a response by passing a RequestContext...I know...it can be done with just 1 line in the body on the function but this is another way...and could be useful for someone :=)

urls.py

# ...imports and other stuff....

# This is really important when we set DEBUG = False on settings.py to define custom error pages....
handler404 = 'my_app_name.views.not_found_404'
handler500 = 'my_app_name.views.internal_error_500'


# ...urlpatterns and another stuff....

views.py

from django.template import RequestContext, loader
from django import http


def not_found_404(request, template_name='system/not_found.html'):
    t = loader.get_template(template_name)
    return http.HttpResponseNotFound(t.render(RequestContext(request,{'request_path': request.path})))
    
def internal_error_500(request):
    return render(request, 'system/internal_error.html')  # as you can see...this is another way to call a template for a view...