django admin filter for GenericForeignKey field

admin.py

# https://djangosnippets.org/snippets/10564/

list_filter = [
        'name',
        get_generic_foreign_key_filter(
            u'Filter Target',
            content_type_id_field='target_ct',
            object_id_field='target_id'
        )
    ]

def get_generic_foreign_key_filter(title, parameter_name=u'', separator='-', content_type_id_field='content_type_id', object_id_field='object_id') :

    class GenericForeignKeyFilter(SimpleListFilter):

        def __init__(self, request, params, model, model_admin):
            self.separator = separator
            self.title = title
            self.parameter_name = u'generic_foreign_key_' + parameter_name
            super(GenericForeignKeyFilter, self).__init__(request, params, model, model_admin)

        def lookups(self, request, model_admin):
            variable_column = object_id_field
            search_type = 'isnull'
            filter = variable_column + '__' + search_type
            qs = model_admin.model.objects.exclude(**{ filter: True })\
                .order_by(content_type_id_field, object_id_field)\
                .distinct(content_type_id_field, object_id_field)\
                .values_list(content_type_id_field, object_id_field)
            return [
                (
                    '{1}{0.separator}{2}'.format(self, *content_type_and_obj_id_pair),
                    ContentType.objects
                        .get(id=content_type_and_obj_id_pair[0])
                        .model_class()
                        .objects.get(pk=content_type_and_obj_id_pair[1])
                        .__str__()
                )
                for content_type_and_obj_id_pair
                in qs
            ]

        def queryset(self, request, queryset):
            try :
                content_type_id, object_id = self.value().split(self.separator)
                return queryset.filter(**({
                    content_type_id_field:content_type_id,
                    object_id_field:object_id
                }))
            except:
                return queryset

    return GenericForeignKeyFilter