fix the wrong type

Author: RaviTezu

ignite/contrib/handlers/base_logger.py

@@ -1,7 +1,7 @@
 import numbers
 import warnings
 from abc import ABCMeta, abstractmethod
-from typing import Any, Callable, List, Mapping, Optional, Sequence
+from typing import Any, Callable, List, Mapping, Optional, Sequence, Union
 
 import torch
 from torch.optim import Optimizer
@@ -43,7 +43,7 @@ class BaseOutputHandler(BaseHandler):
     def __init__(
         self,
         tag,
-        metric_names: Optional[str, List[str]] = None,
+        metric_names: Optional[Union[str, List[str]]] = None,
         output_transform: Optional[Callable] = None,
         global_step_transform: Optional[Callable] = None,
     ):

ignite/contrib/handlers/mlflow_logger.py

@@ -1,6 +1,6 @@
 import numbers
 import warnings
-from typing import Any, Callable, List, Mapping, Optional
+from typing import Any, Callable, List, Mapping, Optional, Union
 
 import torch
 from torch.optim import Optimizer
@@ -209,7 +209,7 @@ def global_step_transform(engine, event_name):
     def __init__(
         self,
         tag: str,
-        metric_names: Optional[str, List[str]] = None,
+        metric_names: Optional[Union[str, List[str]]] = None,
         output_transform: Optional[Callable] = None,
         global_step_transform: Optional[Callable] = None,
     ):

ignite/contrib/handlers/neptune_logger.py

@@ -1,7 +1,7 @@
 import numbers
 import tempfile
 import warnings
-from typing import Any, Callable, List, Mapping, Optional
+from typing import Any, Callable, List, Mapping, Optional, Union
 
 import torch
 from torch.nn import Module
@@ -320,7 +320,7 @@ def global_step_transform(engine, event_name):
     def __init__(
         self,
         tag: str,
-        metric_names: Optional[str, List[str]] = None,
+        metric_names: Optional[Union[str, List[str]]] = None,
         output_transform: Optional[Callable] = None,
         global_step_transform: Optional[Callable] = None,
     ):