human
I wrote the below code

    def _execute(pkg):
        when = kwargs.pop('when', pkg.name)
        _depends_on(pkg, spec, when=when)
        pkg.extendees[spec] = (Spec(spec), kwargs)
    return _execute

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

@directive(('extendees', 'dependencies', 'dependency_types'))
def extends(spec, **kwargs):