code: def comparelist_view(self, request, object_id, extra_context=None):
          
          opts = self.model._meta
          object_id = unquote(object_id)
          current = get_object_or_404(self.model, pk=object_id)
          # As done by reversion's history_view
          action_list = [
              {
                  "revision": version.revision,
                  "url": reverse("%s:%s_%s_compare" % (self.admin_site.name, opts.app_label, opts.model_name), args=(quote(version.object_id), version.id)),
              } for version in self._reversion_order_version_queryset(Version.objects.get_for_object_reference(
                  self.model,
                  object_id).select_related("revision__user"))]
          context = {"action_list": action_list,
                     "opts": opts,
                     "object_id": quote(object_id),
                     "original": current,
                    }
          extra_context = extra_context or {}
          context.update(extra_context)
          return render(request, self.compare_list_template or self._get_template_list("compare_list.html"),
                        context)
docs: Allow selecting versions to compare.