'DataLoader' object has no attribute 'federate'

Question

I want to get a federated dataset with pytorch so I write this :

training_dataset = datasets.ImageFolder(\data)
train_set = torch.utils.data.DataLoader(training_dataset, batch_size=20, shuffle=True)
base_federated=train_set.federate((bob, alice))
federated_train_loader = sy.FederatedDataLoader( # <-- this is now a FederatedDataLoader 
                         base_federated,batch_size=args.batch_size)

The error was :

AttributeError: 'DataLoader' object has no attribute 'federate'

So how can I get a torch.utils.Dataset instead of torch.utils.DataLoader knowing that my dataset is an image dataset.