Replace assertions with ValueError exception (#14142)

Updated masked-language modeling examples in pytorch
with convention defined by #12789

examples/pytorch/language-modeling/run_mlm.py

@@ -188,10 +188,12 @@ class DataTrainingArguments:
         else:
             if self.train_file is not None:
                 extension = self.train_file.split(".")[-1]
-                assert extension in ["csv", "json", "txt"], "`train_file` should be a csv, a json or a txt file."
+                if extension not in ["csv", "json", "txt"]:
+                    raise ValueError("`train_file` should be a csv, a json or a txt file.")
             if self.validation_file is not None:
                 extension = self.validation_file.split(".")[-1]
-                assert extension in ["csv", "json", "txt"], "`validation_file` should be a csv, a json or a txt file."
+                if extension not in ["csv", "json", "txt"]:
+                    raise ValueError("`validation_file` should be a csv, a json or a txt file.")
 
 
 def main():

examples/pytorch/language-modeling/run_mlm_no_trainer.py

@@ -201,10 +201,12 @@ def parse_args():
     else:
         if args.train_file is not None:
             extension = args.train_file.split(".")[-1]
-            assert extension in ["csv", "json", "txt"], "`train_file` should be a csv, json or txt file."
+            if extension not in ["csv", "json", "txt"]:
+                raise ValueError("`train_file` should be a csv, json or txt file.")
         if args.validation_file is not None:
             extension = args.validation_file.split(".")[-1]
-            assert extension in ["csv", "json", "txt"], "`validation_file` should be a csv, json or txt file."
+            if extension not in ["csv", "json", "txt"]:
+                raise ValueError("`validation_file` should be a csv, json or txt file.")
 
     if args.push_to_hub:
         assert args.output_dir is not None, "Need an `output_dir` to create a repo when `--push_to_hub` is passed."