def METHOD_NAME(self, product_type_name, *args, **kwargs):
    """ Handle the listing of mask types
    """
    try:
        product_type = models.ProductType.objects.get(name=product_type_name)
    except models.ProductType.DoesNotExist:
        raise CommandError('No such product type %r' % product_type_name)
    for mask_type in product_type.mask_types.all():
        print("%s %s" % (mask_type.name, '(validity)' if mask_type.validity else ''))