def get_inventory(self):
        if len(self.resource_groups) > 0:
            # get VMs for requested resource groups
            for resource_group in self.resource_groups:
                try:
                    virtual_machines = self._compute_client.virtual_machines.list(resource_group)
                except Exception as exc:
                    sys.exit("Error: fetching virtual machines for resource group {0} - {1}".format(resource_group, str(exc)))
                if self._args.host or self.tags:
                    selected_machines = self._selected_machines(virtual_machines)
                    self._load_machines(selected_machines)
                else:
                    self._load_machines(virtual_machines)
        else:
            # get all VMs within the subscription
            try:
                virtual_machines = self._compute_client.virtual_machines.list_all()
            except Exception as exc:
                sys.exit("Error: fetching virtual machines - {0}".format(str(exc)))

            if self._args.host or self.tags or self.locations:
                selected_machines = self._selected_machines(virtual_machines)
                self._load_machines(selected_machines)
            else:
                self._load_machines(virtual_machines)