[Trainer] Fix _rotate_checkpoints

Close #3920

src/transformers/trainer.py

@@ -434,13 +434,13 @@ class Trainer:
     def _sorted_checkpoints(self, checkpoint_prefix=PREFIX_CHECKPOINT_DIR, use_mtime=False) -> List[str]:
         ordering_and_checkpoint_path = []
 
-        glob_checkpoints = Path(self.args.output_dir).glob(f"{checkpoint_prefix}-*")
+        glob_checkpoints = [str(x) for x in Path(self.args.output_dir).glob(f"{checkpoint_prefix}-*")]
 
         for path in glob_checkpoints:
             if use_mtime:
                 ordering_and_checkpoint_path.append((os.path.getmtime(path), path))
             else:
-                regex_match = re.match(".*{}-([0-9]+)".format(checkpoint_prefix), path)
+                regex_match = re.match(f".*{checkpoint_prefix}-([0-9]+)", path)
                 if regex_match and regex_match.groups():
                     ordering_and_checkpoint_path.append((int(regex_match.groups()[0]), path))
 
@@ -449,9 +449,7 @@ class Trainer:
         return checkpoints_sorted
 
     def _rotate_checkpoints(self, use_mtime=False) -> None:
-        if not self.args.save_total_limit:
-            return
-        if self.args.save_total_limit <= 0:
+        if self.args.save_total_limit is None or self.args.save_total_limit <= 0:
             return
 
         # Check if we should delete older checkpoint(s)