examples/pytorch/image-classification/run_image_classification.py/DataTrainingArguments/__post_init__
class DataTrainingArguments:    def __post_init__(self):
        data_files = dict()
        if self.train_dir is not None:
            data_files["train"] = self.train_dir
        if self.validation_dir is not None:
            data_files["val"] = self.validation_dir
        self.data_files = data_files if data_files else None