comments and cleanup

ml-agents/mlagents/tf_utils/globals.py

 from typing import Optional
 
 _rank: Optional[int] = None
-_local_rank: Optional[int] = None
+    """
+    Returns the rank (in the MPI sense) of the current process.
+    For local training, this will always be None.
+    If this needs to be used, it should be done from outside ml-agents.
+    :return:
+    """
     return _rank

ml-agents/mlagents/trainers/policy/tf_policy.py

     functions to save/load models and create the input placeholders.
     """
 
-    broadcast_global_variables: Callable[[int], None] = lambda x: None
+    # Callback function used at the start of training to synchronize weights.
+    # By default, this nothing.
+    # If this needs to be used, it should be done from outside ml-agents.
+    broadcast_global_variables: Callable[[int], None] = lambda root_rank: None
 
     def __init__(
         self,