blog_2.py

class MNISTDataModule(pl.LightningDataModule):

    def __init__(self, data_dir: str = PATH, batch_size):
        super().__init__()
        self.batch_size = batch_size

    def setup(self, stage=None):
        self.mnist_test = MNIST(self.data_dir, train=False)
        mnist_full = MNIST(self.data_dir, train=True)
        self.mnist_train, self.mnist_val = random_split(mnist_full, [55000, 5000])

    def train_dataloader(self):
        return DataLoader(self.mnist_train, batch_size=self.batch_size)

    def val_dataloader(self):
        return DataLoader(self.mnist_val, batch_size=self.batch_size)

    def test_dataloader(self):
        return DataLoader(self.mnist_test, batch_size=self.batch_size)