'INTERNAL USE ONLY. DO NOT USE THIS OUTSIDE THIS CLASS!'

def __render_composite(self, book_id, mi, formatter, template_cache):

    ans = formatter.safe_format(self.metadata[u'display'][u'composite_template'], mi, _(u'TEMPLATE    ERROR'), mi, column_name=self._composite_name, template_cache=template_cache, template_functions=self.get_template_functions()).strip()
    with self._lock:
        self._render_cache[book_id] = ans
    return ans
