ds_name will never be None here, 

1) If no args is being passed to the method, it will pick the ds_name value from 
self.distributor_name = conf.properties['stageportal.distributor.name'] that is the conf file and 
this is the default behaviour.

2) But if we pass an argument, that will be picked instead.

3) ds.distributor_name and ds.quantity both have similar implementation.