我创建了一个自定义的Dataset类，它继承自PyTorch的Dataset类，以便处理我已经预处理的自定义数据集。

当我尝试创建DataLoader对象时，遇到了以下错误：

/usr/local/lib/python3.6/dist-packages/torch/utils/data/dataloader.py in __init__(self, dataset, batch_size, shuffle, sampler, batch_sampler, num_workers, collate_fn, pin_memory, drop_last, timeout, worker_init_fn)    174             if sampler is None:    175                 if shuffle:--> 176                     sampler = RandomSampler(dataset)    177                 else:    178                     sampler = SequentialSampler(dataset)/usr/local/lib/python3.6/dist-packages/torch/utils/data/sampler.py in __init__(self, data_source, replacement, num_samples)     62                              "since a random permute will be performed.")     63 ---> 64         if not isinstance(self.num_samples, int) or self.num_samples <= 0:     65             raise ValueError("num_samples should be a positive integer "     66                              "value, but got num_samples={}".format(self.num_samples))/usr/local/lib/python3.6/dist-packages/torch/utils/data/sampler.py in num_samples(self)     70         # dataset size might change at runtime     71         if self._num_samples is None:---> 72             return len(self.data_source)     73         return self._num_samples     74 /usr/local/lib/python3.6/dist-packages/torch/utils/data/dataset.py in __len__(self)     18      19     def __len__(self):---> 20         raise NotImplementedError     21      22     def __add__(self, other):NotImplementedError: 

所以，错误信息是关于dataset.py中len()函数未实现，对吗？但我确实实现了它，还有getitem()和init()函数。

我该如何解决这个问题？谢谢

回答：

请确保代码中的名称正确。它应该是__len__。