'Helper method to render an options group
@param group: the group as dict {label:label, items:[items]}'

def _render_group(self, group):

    items = group['items']
    if items:
        label = group['label']
        render_item = self._render_item
        options = [render_item(i) for i in items]
        if label:
            return [OPTGROUP(options, _label=label)]
        else:
            return options
    else:
        return None
