如何修复 ValueError：解包的值太多（预期为 2）？

Question

最近遇到这样一个问题：ValueError: too many values to unpack (expected 2).

import os
import natsort
from PIL import Image
import torchvision
import torch
import torch.optim as optim
from torchvision import transforms, models
from torch.utils.data import DataLoader, Dataset
import torch.nn as nn
import torch.nn.functional as F

root_dir = './images/'

class Col(Dataset):
    def __init__(self, main_dir, transform):
        self.main_dir = main_dir
        self.transform = transform
        all_images = self.all_img(main_dir = main_dir)
        self.total_imges = natsort.natsorted(all_images)
 
    def __len__(self):
        return len(self.total_imges)
 
    def __getitem__(self, idx):
        img_loc = os.path.join(self.total_imges[idx])
        image = Image.open(img_loc).convert("RGB")
        tensor_image = self.transform(image)
        return tensor_image
 
    def all_img(self, main_dir):
        img = []     
        for path, subdirs, files in os.walk(main_dir):
            for name in files:
                img.append(os.path.join(path, name))
        return img

model = models.resnet18(pretrained=False)
model.fc = nn.Sequential(nn.Linear(model.fc.in_features, 256),
                         nn.ReLU(),
                         nn.Dropout(p=0.3),
                         nn.Linear(256, 100),
                         nn.ReLU(),
                         nn.Dropout(p=0.4),
                         nn.Linear(100,9))
# model.load_state_dict(torch.load('model.pth'))

for name, param in model.named_parameters():
    if("bn" not in name):
        param.requires_grad = False

transform = transforms.Compose([
    transforms.Resize((224, 224)),
    transforms.ToTensor(),
    transforms.Normalize(mean=[0.5457, 0.5457, 0.5457], std=[0.2342, 0.2342, 0.2342])    
])
 
data = Col(main_dir=root_dir, transform=transform)
 
dataset = torch.utils.data.DataLoader(data, batch_size=130)
 
train_set, validate_set= torch.utils.data.random_split(dataset, [round(len(dataset)*0.7), (len(dataset) - round(len(dataset)*0.7))])

if torch.cuda.is_available():
    device = torch.device("cuda") 
else:
    device = torch.device("cpu")
 
model.to(device)

def train(model, optimizer, loss_fn, train_set, validate_set, epochs=20, device="cpu"):
    for epoch in range(1, epochs+1):
        training_loss = 0.0
        valid_loss = 0.0
        model.train()
        for batch in train_set:
            optimizer.zero_grad()
            inputs, targets = batch
            inputs = inputs.to(device)
            targets = targets.to(device)
            output = model(inputs)
            loss = loss_fn(output, targets)
            loss.backward()
            optimizer.step()
            training_loss += loss.data.item() * inputs.size(0)
        training_loss /= len(train_set.dataset)
 
        model.eval()
        num_correct = 0 
        num_examples = 0
        for batch in validate_set:
            inputs, targets = batch
            inputs = inputs.to(device)
            output = model(inputs)
            targets = targets.to(device)
            loss = loss_fn(output,targets) 
            valid_loss += loss.data.item() * inputs.size(0)
            correct = torch.eq(torch.max(F.softmax(output, dim=1), dim=1)[1], targets)
            num_correct += torch.sum(correct).item()
            num_examples += correct.shape[0]
        valid_loss /= len(validate_set.dataset)
 
        print('Epoch: {}, Training Loss: {:.2f}, Validation Loss: {:.2f}, accuracy = {:.2f}'.format(epoch, training_loss,
        valid_loss, num_correct / num_examples))
 
optimizer = optim.Adam(model.parameters(), lr=0.0001)

但是调用这个函数

train(model, optimizer,torch.nn.CrossEntropyLoss(), train_set.dataset, validate_set.dataset, epochs=100, device=device)

给出这个错误

---------------------------------------------------------------------------
ValueError                                Traceback (most recent call last)
/tmp/ipykernel_4828/634509595.py in <module>
----> 1 train(model, optimizer,torch.nn.CrossEntropyLoss(), train_set.dataset, validate_set.dataset, epochs=100, device=device)
 
/tmp/ipykernel_4828/1473922939.py in train(model, optimizer, loss_fn, train_set, validate_set, epochs, device)
      6         for batch in train_set:
      7             optimizer.zero_grad()
----> 8             inputs, targets = batch
      9             inputs = inputs.to(device)
     10             targets = targets.to(device)
 
ValueError: too many values to unpack (expected 2)

Answer 1

批处理不包含输入和目标。您的问题只是 getitem 仅返回 tensor_image （大概是输入），而不是任何目标。