views.py

class CategoryList(ListView):
    template_name = 'app/categories.html'
    model = Category
    def get_queryset(self):
        self.category = get_object_or_404(Category, slug=self.args[0])
        return Category.objects.filter(category=self.category)

viewsiwant.py

class CategoryList(ListView):
    template_name = 'app/categories.html'
    model = Category
    def get_queryset(self):
        self.category = get_object_or_404(Category, slug=self.args[0])
        return Category.objects.filter(category=self.category), Item.objects.filter(category=self.category)