Allow custom actions

stdlib/3/argparse.pyi

@@ -2,7 +2,7 @@
 #
 # NOTE: This dynamically typed stub was automatically generated by stubgen.
 
-from typing import Any, Sequence
+from typing import Any, Sequence, Union
 
 SUPPRESS = ... # type: Any
 OPTIONAL = ... # type: Any
@@ -118,7 +118,7 @@ class _ActionsContainer:
     def get_default(self, dest): ...
     def add_argument(self,
         *args: str,
-        action: str = ...,
+        action: Union[str, Action] = ...,
         nargs: str = ...,
         const: Any = ...,
         default: Any = ...,