To do multiple steps, we implement a function the_loop that iterates over a dataloader. It should do a training step per batch for epochs. After one epoch, the loss on the validation set should be calculated.帮我根据这个要求补充完整下面代码中。。。的部分。 def the_loop(net, optimizer, train_loader, val_loader=None, epochs=None, swa_model=None, swa_start=5): if epochs is None: raise Exception("a training duration must be given: set epochs") log_iterval = 1 running_mean = 0. loss = Tensor([0.]).cuda() losses = [] val_losses = [] states = [] i, j = 0, 0 pbar = tqdm(train_loader, desc=f"epoch {i}", postfix={"loss": loss.item(), "step": j}) for i in range(epochs): running_mean = 0. j = 0 pbar.set_description(f"epoch {i}") pbar.refresh() pbar.reset() for j, batch in enumerate(train_loader): # implement training step by # - appending the current states to `states` # - doing a training_step # - appending the current loss to the `losses` list # - update the running_mean for logging ... if j % log_iterval == 0 and j != 0: pbar.set_postfix({"loss": running_mean.item(), "step": j}) running_mean = 0. pbar.update() if i > swa_start and swa_model is not None: swa_model.update_parameters(net) if val_loader is not None: # evaluate the current net on the validation data loader and # collect all losses in the ´val_loss´ list ... pbar.refresh() if val_loader is not None: return losses, states, val_losses return losses, states

Here is the completed code:

def the_loop(net, optimizer, train_loader, val_loader=None, epochs=None, swa_model=None, swa_start=5):
    if epochs is None:
        raise Exception("a training duration must be given: set epochs")
    
    log_iterval = 1
    running_mean = 0.
    loss = torch.Tensor([0.]).cuda()
    
    losses = []
    val_losses = []
    states = []
    i, j = 0, 0
    
    pbar = tqdm(train_loader, desc=f"epoch {i}", postfix={"loss": loss.item(), "step": j})
    
    for i in range(epochs):
        running_mean = 0.
        j = 0
        
        pbar.set_description(f"epoch {i}")
        pbar.refresh()
        pbar.reset()
        
        for j, batch in enumerate(train_loader):
            # implement training step by
            # - appending the current states to `states`
            # - doing a training_step
            # - appending the current loss to the `losses` list
            # - update the running_mean for logging
            
            states.append(net.state_dict())
            
            optimizer.zero_grad()
            output = net(batch)
            batch_loss = loss_function(output, batch.target)
            batch_loss.backward()
            optimizer.step()
            
            losses.append(batch_loss.item())
            running_mean = (running_mean * j + batch_loss.item()) / (j + 1)
            
            if j % log_iterval == 0 and j != 0:
                pbar.set_postfix({"loss": running_mean, "step": j})
                running_mean = 0.
            
            pbar.update()
        
        if i > swa_start and swa_model is not None:
            swa_model.update_parameters(net)
        
        if val_loader is not None:
            val_loss = 0.
            with torch.no_grad():
                for val_batch in val_loader:
                    val_output = net(val_batch)
                    val_loss += loss_function(val_output, val_batch.target).item()
            val_loss /= len(val_loader)
            val_losses.append(val_loss)
    
    pbar.refresh()
    
    if val_loader is not None:
        return losses, states, val_losses
    
    return losses, states

Note that the training step implementation assumes that you have already defined a `loss_function` and that the batch data has an attribute named `target` that contains the ground truth labels.