my dataset has forty thousands images, but I do not know how to put my data into the neural network.I have four classes, every class in the same folder, so I have four folders .So how do I label the image?
Write a custom Dataset (http://pytorch.org/docs/0.2.0/data.html#torch.utils.data.Dataset) and use DataLoader to load it. 
Actually, this may also just work (and is simpler) http://pytorch.org/docs/0.2.0/torchvision/datasets.html#torchvision.datasets.ImageFolder
okay，thanks very much