independent training / eval with local files (#10710)

* independent training / eval with local files

* remove redundant assert

examples/question-answering/run_qa.py

@@ -242,9 +242,12 @@ def main():
         data_files = {}
         if data_args.train_file is not None:
             data_files["train"] = data_args.train_file
+            extension = data_args.train_file.split(".")[-1]
+
         if data_args.validation_file is not None:
             data_files["validation"] = data_args.validation_file
-        extension = data_args.train_file.split(".")[-1]
+            extension = data_args.validation_file.split(".")[-1]
+
         datasets = load_dataset(extension, data_files=data_files, field="data")
     # See more about loading any type of standard or custom dataset (from files, python dict, pandas DataFrame, etc) at
     # https://huggingface.co/docs/datasets/loading_datasets.html.