human
Complete the below
@directive(('extendees', 'dependencies', 'dependency_types'))
def extends(spec, **kwargs):

    ''''Same as depends_on, but dependency is symlinked into parent prefix.
    This is for Python and other language modules where the module
    needs to be installed into the prefix of the Python installation.
    Spack handles this by installing modules into their own prefix,
    but allowing ONE module version to be symlinked into a parent
    Python install at a time.
    keyword arguments can be passed to extends() so that extension
    packages can pass parameters to the extendee\'s extension
    mechanism.'
    '''
assistant
#Here is Python program to fix of the Python installation.
    def _execute(pkg):
        when = kwargs.pop('when', pkg.name)
        _depends_on(pkg, spec, when=when)
        pkg.extendees[spec] = (Spec(spec), kwargs)
    return _execute