examples/tensorflow/text-classification/run_text_classification.py/DataTrainingArguments/__post_init__
class DataTrainingArguments:    def __post_init__(self):
        train_extension = self.train_file.split(".")[-1].lower() if self.train_file is not None else None
        validation_extension = (
            self.validation_file.split(".")[-1].lower() if self.validation_file is not None else None
        )
        test_extension = self.test_file.split(".")[-1].lower() if self.test_file is not None else None
        extensions = {train_extension, validation_extension, test_extension}
        extensions.discard(None)
        assert len(extensions) != 0, "Need to supply at least one of --train_file, --validation_file or --test_file!"
        assert len(extensions) == 1, "All input files should have the same file extension, either csv or json!"
        assert "csv" in extensions or "json" in extensions, "Input files should have either .csv or .json extensions!"
        self.input_file_extension = extensions.pop()