使用torch.utils.data的数据集和数据加载器加载数据时发生错误。 TypeError：“类型”类型的对象没有len（）

Question

我遇到以下错误：

TypeError: object of type 'type' has no len()

我认为错误是在加载图像数据集时发生的。这个错误是什么意思？

我已经在github或网上搜索了很多示例，没有我真正想要的示例。

代码是：

class MakeDataSet(Dataset):
    def __init__(self, data_path, transform=None):
        self.file_names = glob(data_path)
        self.labels = []
        self.transform = transform
        for LA in self.file_names:
            if 'cat' in LA:
                self.labels.append(0)
            if 'dog' in LA:
                self.labels.append(1)

    def __getitem__(self, index):
        img = Image.open(self.file_names[index])
        if self.transform is not None:
            img = self.transform(img)

        label = torch.from_numpy(np.array(self.labels[index]))
        return img, label

    def __len__(self):
        return len(self.file_names)


transformation = transforms.Compose([transforms.ToTensor()])
DB = MakeDataSet(img_path, transform=transformation)
loader = DataLoader(MakeDataSet, batch_size=5, shuffle=True)

完整的错误消息是：

File "C:\Program Files\JetBrains\PyCharm Community Edition 2018.3\helpers\pydev\pydevd.py", line 1689, in <module>
    main()
  File "C:\Program Files\JetBrains\PyCharm Community Edition 2018.3\helpers\pydev\pydevd.py", line 1683, in main
    globals = debugger.run(setup['file'], None, None, is_module)
  File "C:\Program Files\JetBrains\PyCharm Community Edition 2018.3\helpers\pydev\pydevd.py", line 1083, in run
    pydev_imports.execfile(file, globals, locals)  # execute the script
  File "C:\Program Files\JetBrains\PyCharm Community Edition 2018.3\helpers\pydev\_pydev_imps\_pydev_execfile.py", line 18, in execfile
    exec(compile(contents+"\n", file, 'exec'), glob, loc)
  File "C:/Users/BJ/PycharmProjects/AlexNet/test.py", line 45, in <module>
    loader = DataLoader(MakeDataSet, batch_size=5, shuffle=True)
  File "C:\Users\BJ\Anaconda3\envs\install_pytorch\lib\site-packages\torch\utils\data\dataloader.py", line 802, in __init__
    sampler = RandomSampler(dataset)
  File "C:\Users\BJ\Anaconda3\envs\install_pytorch\lib\site-packages\torch\utils\data\sampler.py", line 60, in __init__
    self.num_samples = len(self.data_source)
TypeError: object of type 'type' has no len()