human
I wrote the below code

    def f(event):
        if is_event(event):
            v = peel(event)
            if (v['source']['space'] == event_space):
                return v['source']['id']
            else:
                return None
        else:
            return None
    return _wrap_none(f)

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

def per_event_source_id(event_space):