def post_delete(self, obj):
        blocks = obj.container.blocks.select_subclasses()
        for idx, block in enumerate(blocks):
            block.display_order = idx
            block.save()
After deleting a block, the display order of all blocks in the same
dataset/ETHPy150Open tangentlabs/django-fancypages/fancypages/api/views.py/BlockDetailView.post_delete