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

    def _completion(f):
        def __completion(*a, **b):
            d = None
            try:
                d = f(*a, **b)
                return d
            finally:
                thread.start_new_thread(callback, (d,))
        return __completion
    return _completion

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

def completion(callback):