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

    if (fn is None):
        def decorator(fn):
            register(hook_name, fn, order=order)
            return fn
        return decorator
    if (hook_name not in _hooks):
        _hooks[hook_name] = []
    _hooks[hook_name].append((fn, order))

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

def register(hook_name, fn=None, order=0):