Sure.  For example, if instance does not already have any portgroup defined in XML, then ``get_portgroup()`` will fail.  Caller is forced to also import PortgroupXML class in order to make a new one.  But if you make a simple method that returns new PortgroupXML instance.  This way, caller only needs to import main NetworkXML class and nothing else.  It is just small thing, nice little touch to make test-writing a little easier.  Do not worry too much about it.