def action_checkbox(self, obj):
        """
        A list_display column containing a checkbox widget.
        """
        if self.check_concurrent_action:
            return helpers.checkbox.render(helpers.ACTION_CHECKBOX_NAME,
                                           force_text("%s,%s" % (obj.pk,
                                                                 get_revision_of_object(obj))))
        else:  # pragma: no cover
            return super(ConcurrencyActionMixin, self).action_checkbox(obj)
A list_display column containing a checkbox widget.