def list(self, mask=None):
        """List existing placement groups

        Calls SoftLayer_Account::getPlacementGroups
         """
        if mask is None:
            mask = "mask[id, name, createDate, rule, guestCount, backendRouter[id, hostname]]"
        groups = self.client.call('Account', 'getPlacementGroups', mask=mask, iter=True)
        return groups
List existing placement groups

        Calls SoftLayer_Account::getPlacementGroups