After modifying the path, I still get the same error. There are pictures under this path. In addition, where should I print the length of the data set?
# Training data loader
dataloader = DataLoader(
    ImageDataset("F:/CycleGAN/datasets/datasets-master/horse2zebra/train/%s" % opt.dataset_name, transforms_=transforms_, unaligned=True),
    batch_size=opt.batch_size,
    shuffle=True,
    num_workers=opt.n_cpu,
)
# Test data loader
val_dataloader = DataLoader(
    ImageDataset("F:/CycleGAN/datasets/datasets-master/horse2zebra/test/%s" % opt.dataset_name, transforms_=transforms_, unaligned=True, mode="test"),
    batch_size=5,
    shuffle=True,
    num_workers=1,
)

class ImageDataset(Dataset):
    def __init__(self, root, transforms_=None, unaligned=False, mode="train"):
        self.transform = transforms.Compose(transforms_)
        self.unaligned = unaligned

        self.files_A = sorted(glob.glob(os.path.join(root, "%s/A" % mode) + "/*.*"))
        self.files_B = sorted(glob.glob(os.path.join(root, "%s/B" % mode) + "/*.*"))

    def __getitem__(self, index):
        image_A = Image.open(self.files_A[index % len(self.files_A)])

        if self.unaligned:
            image_B = Image.open(self.files_B[random.randint(0, len(self.files_B) - 1)])
        else:
            image_B = Image.open(self.files_B[index % len(self.files_B)])

        # Convert grayscale images to rgb
        if image_A.mode != "RGB":
            image_A = to_rgb(image_A)
        if image_B.mode != "RGB":
            image_B = to_rgb(image_B)

        item_A = self.transform(image_A)
        item_B = self.transform(image_B)
        return {"A": item_A, "B": item_B}

    def __len__(self):
        return max(len(self.files_A), len(self.files_B))