Here you go:
class NotMNISTDataLoader(BaseDataLoader):
    """
    NotMnist data loading demo using BaseDataLoader
    """
    def __init__(self, data_dir, batch_size, shuffle, validation_split, num_workers, training=True):
        print("NotMnist is used")
        self.data_dir = data_dir + "NotMNIST/"
        
        trsfm = transforms.Compose([
            transforms.Resize((32, 32)),
            transforms.ToTensor(),
            transforms.Normalize((0.1307,), (0.3081,)),
            transforms.Lambda(lambda x: x.repeat(3, 1, 1))
            ])
       
        self.dataset = NotMNIST(self.data_dir, train = training, download = True, transform = trsfm)
        super(NotMNISTDataLoader, self).__init__(self.dataset, batch_size, shuffle, validation_split, num_workers)