human
Here's a good function header given the following:
I wrote the below code

    def _set_ev_cls_dec(handler):
        if ('callers' not in dir(handler)):
            handler.callers = {}
        for e in _listify(ev_cls):
            handler.callers[e] = _Caller(_listify(dispatchers), e.__module__)
        return handler
    return _set_ev_cls_dec

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

def set_ev_cls(ev_cls, dispatchers=None):