def get_vapp_by_name(self, name, datacenter=None, from_mor=None):
        """
        Returns an instance of VIVApp. Where its name matches @name.
        The vApp is searched throughout all the datacenters, unless the name or 
        MOR of the datacenter the vApp belongs to is provided. The first instance
        matching @name is returned. If @from_mor, datacenter is ignored. 
        NOTE: As names might be duplicated is recommended to use get_vm_by_path
        instead.
        """
        if not self.__logged:
            raise VIException("Must call 'connect' before invoking this method",
                              FaultTypes.NOT_CONNECTED)
        try:
            nodes = [None, ]
            if from_mor and VIMor.is_mor(from_mor):
                nodes = [from_mor, ]
            else:
                if datacenter and VIMor.is_mor(datacenter):
                    nodes = [datacenter]
                elif datacenter:
                    dc = self.get_datacenters()
                    nodes = [k for k, v in dc.iteritems() if v == datacenter]

            for node in nodes:
                vms = self._get_managed_objects(MORTypes.VirtualApp,
                                                      from_mor=node)
                for k, v in vms.iteritems():
                    if v == name:
                        return VIVApp(self, k)
        except (VI.ZSI.FaultException), e:
            raise VIApiException(e)

    def handler_delete_snapshot(self, task_id, parameters):
        snapshot_id = parameters['snapshot_id']
        vm_id = parameters['vm_id']
        snapshot_mor = VIMor(snapshot_id, MORTypes.VirtualMachineSnapshot)

        request = VI.RemoveSnapshot_TaskRequestMsg()

        mor_snap = request.new__this(snapshot_mor)
        mor_snap.set_attribute_type(snapshot_mor.get_attribute_type())
        request.set_element__this(mor_snap)
        request.set_element_removeChildren(False)

        TaskStatusHandler.update_task(task_id, 'Starting background task...')

        task = (yield self.application.executor.submit(self.server._proxy.RemoveSnapshot_Task, request))._returnval

        TaskStatusHandler.update_task(task_id, 'Background task started, waiting for completion...')

        vi_task = yield self.application.executor.submit(VITask, task, self.server)

        status = yield self.application.executor.submit(vi_task.wait_for_state, [vi_task.STATE_SUCCESS,
                                                                                 vi_task.STATE_ERROR])

        if status == vi_task.STATE_ERROR:
            raise VIException(vi_task.get_error_message(),
                              FaultTypes.TASK_ERROR)

        TaskStatusHandler.update_task(task_id, 'Snapshot deleted')
        TaskStatusHandler.delete_task(task_id)

        self.send_vm_update(vm_id)

    def register_vm(self, path, name=None, sync_run=True, folder=None,
                    template=False, resourcepool=None, host=None):
        """Adds an existing virtual machine to the folder.
        @path: a datastore path to the virtual machine.
            Example "[datastore] path/to/machine.vmx".
        @name: the name to be assigned to the virtual machine.
            If this parameter is not set, the displayName configuration
            parameter of the virtual machine is used.
        @sync_run: if True (default) waits for the task to finish, and returns
            a VIVirtualMachine instance with the new VM (raises an exception if
            the task didn't succeed). If @sync_run is set to False the task is
            started and a VITask instance is returned
        @folder_name: folder in which to register the virtual machine.
        @template: Flag to specify whether or not the virtual machine
            should be marked as a template.
        @resourcepool: MOR of the resource pool to which the virtual machine should
            be attached. If imported as a template, this parameter is not set.
        @host: The target host on which the virtual machine will run. This
            parameter must specify a host that is a member of the ComputeResource
            indirectly specified by the pool. For a stand-alone host or a cluster
            with DRS, the parameter can be omitted, and the system selects a default.
        """
        if not folder:
            folders = self._get_managed_objects(MORTypes.Folder)
            folder = [_mor for _mor, _name in folders.iteritems()
                          if _name == 'vm'][0]
        try:
            request = VI.RegisterVM_TaskRequestMsg()
            _this = request.new__this(folder)
            _this.set_attribute_type(folder.get_attribute_type())
            request.set_element__this(_this)
            request.set_element_path(path)
            if name:
                request.set_element_name(name)
            request.set_element_asTemplate(template)
            if resourcepool:
                pool = request.new_pool(resourcepool)
                pool.set_attribute_type(resourcepool.get_attribute_type())
                request.set_element_pool(pool)
            if host:
                if not VIMor.is_mor(host):
                    host = VIMor(host, MORTypes.HostSystem)
                    hs = request.new_host(host)
                    hs.set_attribute_type(host.get_attribute_type())
                    request.set_element_host(hs)

            task = self._proxy.RegisterVM_Task(request)._returnval
            vi_task = VITask(task, self)
            if sync_run:
                status = vi_task.wait_for_state([vi_task.STATE_SUCCESS,
                                                 vi_task.STATE_ERROR])
                if status == vi_task.STATE_ERROR:
                    raise VITaskException(vi_task.info.error)
                return

            return vi_task

        except (VI.ZSI.FaultException), e:
            raise VIApiException(e)

    def _create_filter(self, property_names=[],
                       from_node=None, obj_type='ManagedEntity', partial_updates=True):
        """Creates filter with given parameters and returns its MOR"""
        try:
            if not from_node:
                from_node = self._do_service_content.RootFolder

            elif isinstance(from_node, tuple) and len(from_node) == 2:
                from_node = VIMor(from_node[0], from_node[1])
            elif not VIMor.is_mor(from_node):
                raise VIException("from_node must be a MOR object or a "
                                  "(<str> mor_id, <str> mor_type) tuple",
                                  FaultTypes.PARAMETER_ERROR)

            request = VI.CreateFilterRequestMsg()
            _this = request.new__this(self._do_service_content.PropertyCollector)
            _this.set_attribute_type(MORTypes.PropertyCollector)
            request.set_element__this(_this)
            request.set_element_partialUpdates(partial_updates)

            spec = request.new_spec()
            propSet = spec.new_propSet()
            propSet.set_element_type(obj_type)
            propSet.set_element_pathSet(property_names)
            spec.set_element_propSet([propSet])

            objects_set = self._get_traversal_objects_set(spec, from_node)
            spec.set_element_objectSet(objects_set)
            request.set_element_spec(spec)

            mor = self._proxy.CreateFilter(request)._returnval
            return mor

        except (VI.ZSI.FaultException), e:
            raise VIApiException(e)

    def get_datastore_by_name(self, name, datacenter=None):
        """
        Returns an instance of VIDatastore, where its name matches @name.
        The datastore is searched throughout all the datacenters, unless the
        name or the MOR of the datacenter (the datastore belongs to) is given.
        The first instance matching @name is returned.
        """
        if not self.__logged:
            raise VIException("Must call 'connect' before invoking this method",
                              FaultTypes.NOT_CONNECTED)

        try:
            if datacenter:
                if VIMor.is_mor(datacenter):
                    nodes = [datacenter]
                else:
                    dc = self.get_datacenters()
                    nodes = [(k,v) for k,v in dc.iteritems() if v == datacenter]
            else:
                nodes = self.get_datacenters().iteritems()

            # todo: use self.get_datastores() instead, if possible
            for node in nodes:
                datacenter_mor, datacenter_name = node
                datastores = self._get_managed_objects(MORTypes.Datastore,
                                                       from_mor=datacenter_mor)
                for k,v in datastores.iteritems():
                    if v == name:
                        return VIDatastore(self, datacenter_name, v)

        except (VI.ZSI.FaultException), e:
            raise VIApiException(e)

    def handler_create_snapshot(self, task_id, parameters):
        vm_id = parameters['vm_id']
        snapshot_name = parameters['snapshot_name']
        snapshot_description = parameters['snapshot_description']

        vm_mor = VIMor(vm_id, MORTypes.VirtualMachine)

        request = VI.CreateSnapshot_TaskRequestMsg()
        mor_vm = request.new__this(vm_mor)
        mor_vm.set_attribute_type(vm_mor.get_attribute_type())
        request.set_element__this(mor_vm)
        request.set_element_name(snapshot_name)
        if snapshot_description:
            request.set_element_description(snapshot_description)
        request.set_element_memory(True)
        request.set_element_quiesce(False)

        vi_task = self.server._proxy.CreateSnapshot_Task(request)._returnval

        vi_task = VITask(vi_task, self.server)

        state = None
        while state not in (vi_task.STATE_SUCCESS, vi_task.STATE_ERROR):
            time.sleep(1)

            state = yield self.application.executor.submit(vi_task.get_state)
            progress = yield self.application.executor.submit(vi_task.get_progress)
            progress = progress or 100
            TaskStatusHandler.update_task(task_id, 'Creating snapshot %s, %d%%...' % (snapshot_name, progress))

        if state == vi_task.STATE_ERROR:
            error_message = yield self.application.executor.submit(vi_task.get_error_message)
            TaskStatusHandler.update_task(task_id, 'Error creating snapshot {0}: {1}'.format(
                snapshot_name, error_message))
            TaskStatusHandler.delete_task(task_id)
            raise Exception(error_message)

        TaskStatusHandler.update_task(task_id, 'Snapshot %s created!' % (snapshot_name,))
        TaskStatusHandler.delete_task(task_id)

        self.send_vm_update(vm_id)

    def handler_revert_to_snapshot(self, task_id, parameters):
        vm_id = parameters['vm_id']
        snapshot_id = parameters['snapshot_id']

        vm_mor = VIMor(vm_id, MORTypes.VirtualMachine)
        snapshot_mor = VIMor(snapshot_id, MORTypes.VirtualMachineSnapshot)

        vm_properties_future = self.application.executor.submit(self.server._get_object_properties, vm_mor, ['name', 'snapshot'])

        request = VI.RevertToSnapshot_TaskRequestMsg()

        mor_snap = request.new__this(snapshot_mor)
        mor_snap.set_attribute_type(snapshot_mor.get_attribute_type())
        request.set_element__this(mor_snap)

        vm_name = None
        snapshot_name = None
        vm_properties = yield vm_properties_future
        for prop in vm_properties.PropSet:
            if prop.Name == 'name':
                vm_name = prop.Val
            elif prop.Name == 'snapshot':
                snapshot_dict = ActionHandler.build_snapshot_dict(prop.Val.RootSnapshotList)
                snapshot_name = snapshot_dict[snapshot_mor].Name

        TaskStatusHandler.update_task(task_id, 'Reverting {0} to {1}...'.format(vm_name, snapshot_name))

        vi_task = self.server._proxy.RevertToSnapshot_Task(request)._returnval

        vi_task = VITask(vi_task, self.server)
        status = yield self.application.executor.submit(
            vi_task.wait_for_state, [vi_task.STATE_SUCCESS,
                                     vi_task.STATE_ERROR])
        if status == vi_task.STATE_ERROR:
            raise VIException(vi_task.get_error_message(),
                              FaultTypes.TASK_ERROR)

        TaskStatusHandler.update_task(task_id, 'Successfully reverted {0} to {1}'.format(vm_name, snapshot_name))
        TaskStatusHandler.delete_task(task_id)

        self.send_vm_update(vm_id)

    def _retrieve_properties_traversal(self, property_names=[],
                                      from_node=None, obj_type='ManagedEntity'):
        """Uses VI API's property collector to retrieve the properties defined
        in @property_names of Managed Objects of type @obj_type ('ManagedEntity'
        by default). Starts the search from the managed object reference
        @from_node (RootFolder by default). Returns the corresponding
        objectContent data object."""
        try:
            if not from_node:
                from_node = self._do_service_content.RootFolder

            elif isinstance(from_node, tuple) and len(from_node) == 2:
                from_node = VIMor(from_node[0], from_node[1])
            elif not VIMor.is_mor(from_node):
                raise VIException("from_node must be a MOR object or a "
                                  "(<str> mor_id, <str> mor_type) tuple",
                                  FaultTypes.PARAMETER_ERROR)

            request, request_call = self._retrieve_property_request()


            _this = request.new__this(
                                     self._do_service_content.PropertyCollector)
            _this.set_attribute_type(MORTypes.PropertyCollector)

            request.set_element__this(_this)
            do_PropertyFilterSpec_specSet = request.new_specSet()

            props_set = []
            do_PropertySpec_propSet = do_PropertyFilterSpec_specSet.new_propSet()
            do_PropertySpec_propSet.set_element_type(obj_type)
            do_PropertySpec_propSet.set_element_pathSet(property_names)
            props_set.append(do_PropertySpec_propSet)

            objects_set = self._get_traversal_objects_set(do_PropertyFilterSpec_specSet, from_node)

            do_PropertyFilterSpec_specSet.set_element_propSet(props_set)
            do_PropertyFilterSpec_specSet.set_element_objectSet(objects_set)
            request.set_element_specSet([do_PropertyFilterSpec_specSet])

            return request_call(request)

        except (VI.ZSI.FaultException), e:
            raise VIApiException(e)

    def _get_vm_for_uuid(self, uuid, datacenter=None):
        """
        Retrieve VM for the provided UUID.

        :type uuid: ``str``
        """
        server = self.connection.client

        dc_list = []
        if datacenter and VIMor.is_mor(datacenter):
            dc_list.append(datacenter)
        else:
            dc = server.get_datacenters()
            if datacenter:
                dc_list = [k for k, v in dc.iteritems() if v == datacenter]
            else:
                dc_list = list(dc.iterkeys())

        for mor_dc in dc_list:
            request = VI.FindByUuidRequestMsg()
            search_index = server._do_service_content.SearchIndex
            mor_search_index = request.new__this(search_index)
            mor_search_index.set_attribute_type(MORTypes.SearchIndex)
            request.set_element__this(mor_search_index)

            mor_datacenter = request.new_datacenter(mor_dc)
            mor_datacenter.set_attribute_type(MORTypes.Datacenter)
            request.set_element_datacenter(mor_datacenter)

            request.set_element_vmSearch(True)
            request.set_element_uuid(uuid)

            try:
                vm = server._proxy.FindByUuid(request)._returnval
            except VI.ZSI.FaultException:
                pass
            else:
                if vm:
                    return VIVirtualMachine(server, vm)

            return None

    def get_vm_by_path(self, path, datacenter=None):
        """Returns an instance of VIVirtualMachine. Where its path matches
        @path. The VM is searched througout all the datacenters, unless the
        name or MOR of the datacenter the VM belongs to is provided."""
        if not self.__logged:
            raise VIException("Must call 'connect' before invoking this method",
                            FaultTypes.NOT_CONNECTED)
        try:
            dc_list = []
            if datacenter and VIMor.is_mor(datacenter):
                dc_list.append(datacenter)
            else:
                dc = self.get_datacenters()
                if datacenter:
                    dc_list = [k for k,v in dc.items() if v==datacenter]
                else:
                    dc_list = list(dc.keys())

            for mor_dc in dc_list:
                request = VI.FindByDatastorePathRequestMsg()
                mor_search_index = request.new__this(
                                           self._do_service_content.SearchIndex)
                mor_search_index.set_attribute_type(MORTypes.SearchIndex)
                request.set_element__this(mor_search_index)
                mor_datacenter = request.new_datacenter(mor_dc)
                mor_datacenter.set_attribute_type(MORTypes.Datacenter)
                request.set_element_datacenter(mor_datacenter)
                request.set_element_path(path)
                try:
                    vm = self._proxy.FindByDatastorePath(request)._returnval
                except VI.ZSI.FaultException:
                    pass
                else:
                    if vm:
                        return VIVirtualMachine(self, vm)
        except (VI.ZSI.FaultException) as e:
            raise VIApiException(e)

        raise VIException("Could not find a VM with path '%s'" % path, 
                          FaultTypes.OBJECT_NOT_FOUND)

    def _retrieve_properties_traversal(self, property_names=[],
                                      from_node=None, obj_type='ManagedEntity'):
        """Uses VI API's property collector to retrieve the properties defined
        in @property_names of Managed Objects of type @obj_type ('ManagedEntity'
        by default). Starts the search from the managed object reference
        @from_node (RootFolder by default). Returns the corresponding
        objectContent data object."""
        try:
            if not from_node:
                from_node = self._do_service_content.RootFolder

            elif isinstance(from_node, tuple) and len(from_node) == 2:
                from_node = VIMor(from_node[0], from_node[1])
            elif not VIMor.is_mor(from_node):
                raise VIException("from_node must be a MOR object or a "
                                  "(<str> mor_id, <str> mor_type) tuple",
                                  FaultTypes.PARAMETER_ERROR)

            request, request_call = self._retrieve_property_request()


            _this = request.new__this(
                                     self._do_service_content.PropertyCollector)
            _this.set_attribute_type(MORTypes.PropertyCollector)

            request.set_element__this(_this)
            do_PropertyFilterSpec_specSet = request.new_specSet()

            props_set = []
            do_PropertySpec_propSet =do_PropertyFilterSpec_specSet.new_propSet()
            do_PropertySpec_propSet.set_element_type(obj_type)
            do_PropertySpec_propSet.set_element_pathSet(property_names)
            props_set.append(do_PropertySpec_propSet)

            objects_set = []
            do_ObjectSpec_objSet = do_PropertyFilterSpec_specSet.new_objectSet()
            mor_obj = do_ObjectSpec_objSet.new_obj(from_node)
            mor_obj.set_attribute_type(from_node.get_attribute_type())
            do_ObjectSpec_objSet.set_element_obj(mor_obj)
            do_ObjectSpec_objSet.set_element_skip(False)

            #Recurse through all ResourcePools
            rp_to_rp = VI.ns0.TraversalSpec_Def('rpToRp').pyclass()
            rp_to_rp.set_element_name('rpToRp')
            rp_to_rp.set_element_type(MORTypes.ResourcePool)
            rp_to_rp.set_element_path('resourcePool')
            rp_to_rp.set_element_skip(False)
            rp_to_vm= VI.ns0.TraversalSpec_Def('rpToVm').pyclass()
            rp_to_vm.set_element_name('rpToVm')
            rp_to_vm.set_element_type(MORTypes.ResourcePool)
            rp_to_vm.set_element_path('vm')
            rp_to_vm.set_element_skip(False)

            spec_array_resource_pool = [do_ObjectSpec_objSet.new_selectSet(),
                                        do_ObjectSpec_objSet.new_selectSet()]
            spec_array_resource_pool[0].set_element_name('rpToRp')
            spec_array_resource_pool[1].set_element_name('rpToVm')

            rp_to_rp.set_element_selectSet(spec_array_resource_pool)

            #Traversal through resource pool branch
            cr_to_rp = VI.ns0.TraversalSpec_Def('crToRp').pyclass()
            cr_to_rp.set_element_name('crToRp')
            cr_to_rp.set_element_type(MORTypes.ComputeResource)
            cr_to_rp.set_element_path('resourcePool')
            cr_to_rp.set_element_skip(False)
            spec_array_computer_resource =[do_ObjectSpec_objSet.new_selectSet(),
                                           do_ObjectSpec_objSet.new_selectSet()]
            spec_array_computer_resource[0].set_element_name('rpToRp');
            spec_array_computer_resource[1].set_element_name('rpToVm');
            cr_to_rp.set_element_selectSet(spec_array_computer_resource)

            #Traversal through host branch
            cr_to_h = VI.ns0.TraversalSpec_Def('crToH').pyclass()
            cr_to_h.set_element_name('crToH')
            cr_to_h.set_element_type(MORTypes.ComputeResource)
            cr_to_h.set_element_path('host')
            cr_to_h.set_element_skip(False)

            #Traversal through hostFolder branch
            dc_to_hf = VI.ns0.TraversalSpec_Def('dcToHf').pyclass()
            dc_to_hf.set_element_name('dcToHf')
            dc_to_hf.set_element_type(MORTypes.Datacenter)
            dc_to_hf.set_element_path('hostFolder')
            dc_to_hf.set_element_skip(False)
            spec_array_datacenter_host = [do_ObjectSpec_objSet.new_selectSet()]
            spec_array_datacenter_host[0].set_element_name('visitFolders')
            dc_to_hf.set_element_selectSet(spec_array_datacenter_host)

            #Traversal through vmFolder branch
            dc_to_vmf = VI.ns0.TraversalSpec_Def('dcToVmf').pyclass()
            dc_to_vmf.set_element_name('dcToVmf')
            dc_to_vmf.set_element_type(MORTypes.Datacenter)
            dc_to_vmf.set_element_path('vmFolder')
            dc_to_vmf.set_element_skip(False)
            spec_array_datacenter_vm = [do_ObjectSpec_objSet.new_selectSet()]
            spec_array_datacenter_vm[0].set_element_name('visitFolders')
            dc_to_vmf.set_element_selectSet(spec_array_datacenter_vm)

            #Traversal through datastore branch
#.........这里部分代码省略.........

    def get_registered_vms(self, datacenter=None, cluster=None,
                           resource_pool=None, status=None,
                           advanced_filters=None):
        """Returns a list of VM Paths.
        @datacenter: name or MORs to filter VMs registered in that datacenter
        @cluster: name or MORs to filter VMs registered in that cluster. If set
            datacenter is ignored.
        @resource_pool: name path or MORs to filter VMs registered in that
            resource pool. If set, both, @datacenter and @cluster are ignored.
        @status: either 'poweredOn', 'poweredOff', or 'suspended' to retrieve
            only VMs in that power state
        @advanced_filters: dictionary
        """

        if not self.__logged:
            raise VIException("Must call 'connect' before invoking this method",
                              FaultTypes.NOT_CONNECTED)
        try:

            if not advanced_filters or not isinstance(advanced_filters, dict):
                advanced_filters={}

            if status:
                advanced_filters['runtime.powerState'] = [status]

            property_filter = list(advanced_filters.iterkeys())

            if not 'config.files.vmPathName' in property_filter:
                property_filter.insert(0, 'config.files.vmPathName')

            #Root MOR filters
            ret = []
            nodes = [None]
            if resource_pool and VIMor.is_mor(resource_pool):
                nodes = [resource_pool]
            elif resource_pool:
                nodes = [k for k,v in self.get_resource_pools().iteritems()
                         if v==resource_pool]
            elif cluster and VIMor.is_mor(cluster):
                nodes = [cluster]
            elif cluster:
                nodes = [k for k,v in self.get_clusters().iteritems()
                        if v==cluster]
            elif datacenter and VIMor.is_mor(datacenter):
                nodes = [datacenter]
            elif datacenter:
                nodes = [k for k,v in self.get_datacenters().iteritems()
                        if v==datacenter]

            for node in nodes:
                obj_content = self._retrieve_properties_traversal(
                                            property_names=property_filter,
                                            from_node=node,
                                            obj_type=MORTypes.VirtualMachine)
                if not obj_content:
                    continue
                for obj in obj_content:
                    try:
                        prop_set = obj.PropSet
                    except AttributeError:
                        continue

                    ppath = None
                    filter_match = dict([(k, False)
                                         for k in advanced_filters.iterkeys()])

                    for item in prop_set:
                        if item.Name == 'config.files.vmPathName':
                            ppath = item.Val
                        elif item.Name in filter_match:
                            expected = advanced_filters.get(item.Name)
                            if not isinstance(expected, list):
                                expected = [expected]
                            if item.Val in expected:
                                filter_match[item.Name] = True

                    if all(filter_match.values()):
                        ret.append(ppath)
            return ret

        except (VI.ZSI.FaultException), e:
            raise VIApiException(e)