human
I wrote the below code

    if before:
        fn_args = list(util.flatten_iterator(inspect_getargspec(method)[0]))
        if isinstance(argument, int):
            pos_arg = argument
            named_arg = (((len(fn_args) > argument) and fn_args[argument]) or None)
        else:
            if (argument in fn_args):
                pos_arg = fn_args.index(argument)
            else:
                pos_arg = None
            named_arg = argument
        del fn_args
    def wrapper(*args, **kw):
        if before:
            if (pos_arg is None):
                if (named_arg not in kw):
                    raise sa_exc.ArgumentError(('Missing    argument    %s' % argument))
                value = kw[named_arg]
            elif (len(args) > pos_arg):
                value = args[pos_arg]
            elif (named_arg in kw):
                value = kw[named_arg]
            else:
                raise sa_exc.ArgumentError(('Missing    argument    %s' % argument))
        initiator = kw.pop('_sa_initiator', None)
        if (initiator is False):
            executor = None
        else:
            executor = args[0]._sa_adapter
        if (before and executor):
            getattr(executor, before)(value, initiator)
        if ((not after) or (not executor)):
            return method(*args, **kw)
        else:
            res = method(*args, **kw)
            if (res is not None):
                getattr(executor, after)(res, initiator)
            return res
    wrapper._sa_instrumented = True
    if hasattr(method, '_sa_instrument_role'):
        wrapper._sa_instrument_role = method._sa_instrument_role
    wrapper.__name__ = method.__name__
    wrapper.__doc__ = method.__doc__
    return wrapper

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

def _instrument_membership_mutator(method, before, argument, after):