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Co-authored-by: Justus Schock <12886177+justusschock@users.noreply.github.com>

pytorch_lightning/callbacks/model_checkpoint.py

@@ -24,7 +24,8 @@
 import re
 import yaml
 from copy import deepcopy
-from typing import Any, Dict, Optional
+from typing import Any, Dict, Optional, Union
+from pathlib import Path
 
 import numpy as np
 import torch
@@ -468,7 +469,7 @@ def on_load_checkpoint(self, checkpointed_state: Dict[str, Any]):
         self.best_model_score = checkpointed_state["best_model_score"]
         self.best_model_path = checkpointed_state["best_model_path"]
 
-    def to_yaml(self, save_path=None):
+    def to_yaml(self, save_path: Optional[Union[str, Path]]=None):
         """ Saves `{'checkpoint_name': score}` dict as a YAML file."""
         best_k = {k: v.item() for k, v in self.best_k_models.items()}
         if save_path is None: