human
I wrote the below code

    def plugin_filter(self):
        return (lambda x: isinstance(x, self._multistanza))
    def plugin_lang_filter(self, lang):
        return (lambda x: (isinstance(x, self._multistanza) and (x[u'lang'] == lang)))
    class Multi(ElementBase, ):
        u'\n                                Template    class    for    multifactory\n                                '
        def setup(self, xml=None):
            self.xml = ET.Element(u'')
    def get_multi(self, lang=None):
        parent = self.parent()
        if ((not lang) or (lang == u'*')):
            res = filter(plugin_filter(self), parent)
        else:
            res = filter(plugin_filter(self, lang), parent)
        return list(res)
    def set_multi(self, val, lang=None):
        parent = self.parent()
        del_multi = getattr(self, (u'del_%s' % plugin_attrib))
        del_multi(lang)
        for sub in val:
            parent.append(sub)
    def del_multi(self, lang=None):
        parent = self.parent()
        if ((not lang) or (lang == u'*')):
            res = filter(plugin_filter(self), parent)
        else:
            res = filter(plugin_filter(self, lang), parent)
        res = list(res)
        if (not res):
            del parent.plugins[(plugin_attrib, None)]
            parent.loaded_plugins.remove(plugin_attrib)
            try:
                parent.xml.remove(self.xml)
            except ValueError:
                pass
        else:
            for stanza in list(res):
                parent.iterables.remove(stanza)
                parent.xml.remove(stanza.xml)
    Multi.is_extension = True
    Multi.plugin_attrib = plugin_attrib
    Multi._multistanza = stanza
    Multi.interfaces = set([plugin_attrib])
    Multi.lang_interfaces = set([plugin_attrib])
    setattr(Multi, (u'get_%s' % plugin_attrib), get_multi)
    setattr(Multi, (u'set_%s' % plugin_attrib), set_multi)
    setattr(Multi, (u'del_%s' % plugin_attrib), del_multi)
    return Multi

What's a good function header?
assistant
#Here's a good function header.

def multifactory(stanza, plugin_attrib):