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   | def create_dataloaders(config):     transform = transforms.Compose([transforms.ToTensor()])     ds_train = torchvision.datasets.MNIST(root="./mnist/",train=True,download=True,transform=transform)     ds_val = torchvision.datasets.MNIST(root="./mnist/",train=False,download=True,transform=transform)
      ds_train_sub = torch.utils.data.Subset(ds_train, indices=range(0, len(ds_train), 5))     dl_train =  torch.utils.data.DataLoader(ds_train_sub, batch_size=config.batch_size, shuffle=True,                                             num_workers=2,drop_last=True)     dl_val =  torch.utils.data.DataLoader(ds_val, batch_size=config.batch_size, shuffle=False,                                            num_workers=2,drop_last=True)     return dl_train,dl_val
  def create_net(config):     net = nn.Sequential()     net.add_module("conv1",nn.Conv2d(in_channels=1,out_channels=config.hidden_layer_width,kernel_size = 3))     net.add_module("pool1",nn.MaxPool2d(kernel_size = 2,stride = 2))      net.add_module("conv2",nn.Conv2d(in_channels=config.hidden_layer_width,                                      out_channels=config.hidden_layer_width,kernel_size = 5))     net.add_module("pool2",nn.MaxPool2d(kernel_size = 2,stride = 2))     net.add_module("dropout",nn.Dropout2d(p = config.dropout_p))     net.add_module("adaptive_pool",nn.AdaptiveMaxPool2d((1,1)))     net.add_module("flatten",nn.Flatten())     net.add_module("linear1",nn.Linear(config.hidden_layer_width,config.hidden_layer_width))     net.add_module("relu",nn.ReLU())     net.add_module("linear2",nn.Linear(config.hidden_layer_width,10))     net.to(device)     return net 
  def train_epoch(model,dl_train,optimizer):     model.train()     for step, batch in enumerate(dl_train):         features,labels = batch         features,labels = features.to(device),labels.to(device)
          preds = model(features)         loss = nn.CrossEntropyLoss()(preds,labels)         loss.backward()
          optimizer.step()         optimizer.zero_grad()     return model
  def eval_epoch(model,dl_val):     model.eval()     accurate = 0     num_elems = 0     for batch in dl_val:         features,labels = batch         features,labels = features.to(device),labels.to(device)         with torch.no_grad():             preds = model(features)         predictions = preds.argmax(dim=-1)         accurate_preds =  (predictions==labels)         num_elems += accurate_preds.shape[0]         accurate += accurate_preds.long().sum()
      val_acc = accurate.item() / num_elems     return val_acc
  def train(config = config):     dl_train, dl_val = create_dataloaders(config)     model = create_net(config);      optimizer = torch.optim.__dict__[config.optim_type](params=model.parameters(), lr=config.lr)          nowtime = datetime.datetime.now().strftime('%Y-%m-%d %H:%M:%S')     wandb.init(project=config.project_name, config = config.__dict__, name = nowtime, save_code=True)     model.run_id = wandb.run.id          model.best_metric = -1.0     for epoch in range(1,config.epochs+1):         model = train_epoch(model,dl_train,optimizer)         val_acc = eval_epoch(model,dl_val)         if val_acc>model.best_metric:             model.best_metric = val_acc             torch.save(model.state_dict(),config.ckpt_path)            nowtime = datetime.datetime.now().strftime('%Y-%m-%d %H:%M:%S')         print(f"epoch【{epoch}】@{nowtime} --> val_acc= {100 * val_acc:.2f}%")                  wandb.log({'epoch':epoch, 'val_acc': val_acc, 'best_val_acc':model.best_metric})                   wandb.finish()          return model   
 
 
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