[RLlib] Make Connector pipeline indexed and individual connetors gett…

…able by int or class (or classname). (#28202)

rllib/connectors/connector.py

@@ -3,7 +3,7 @@
 
 import abc
 import logging
-from typing import TYPE_CHECKING, Any, Dict, List, Tuple
+from typing import TYPE_CHECKING, Any, Dict, List, Tuple, Union
 
 import gym
 
@@ -404,6 +404,44 @@ def __str__(self, indentation: int = 0):
             + [c.__str__(indentation + 4) for c in self.connectors]
         )
 
+    def __getitem__(self, key: Union[str, int, type]):
+        """Returns a list of connectors that fit 'key'.
+
+        If key is a number n, we return a list with the nth element of this pipeline.
+        If key is a Connector class or a string matching the class name of a
+        Connector class, we return a list of all connectors in this pipeline matching
+        the specified class.
+
+        Args:
+            key: The key to index by
+
+        Returns: The Connector at index `key`.
+        """
+        # In case key is a class
+        if not isinstance(key, str):
+            if isinstance(key, slice):
+                raise NotImplementedError(
+                    "Slicing of ConnectorPipeline is currently not supported."
+                )
+            elif isinstance(key, int):
+                return [self.connectors[key]]
+            elif isinstance(key, type):
+                key = key.__name__
+            else:
+                raise NotImplementedError(
+                    "Indexing by {} is currently not supported.".format(type(key))
+                )
+
+        results = []
+        for c in self.connectors:
+            if c.__class__.__name__ == key:
+                results.append(c)
+
+        if len(results) == 0:
+            return []
+
+        return results
+
 
 @PublicAPI(stability="alpha")
 def register_connector(name: str, cls: Connector):

rllib/connectors/tests/test_connector.py

@@ -51,6 +51,10 @@ def test_sanity_check(self):
         self.assertEqual(m.connectors[0].__class__.__name__, "Tom")
         self.assertEqual(m.connectors[1].__class__.__name__, "Mary")
 
+        self.assertEqual(m["Tom"], [m.connectors[0]])
+        self.assertEqual(m[0], [m.connectors[0]])
+        self.assertEqual(m[m.connectors[1].__class__], [m.connectors[1]])
+
 
 if __name__ == "__main__":
     import pytest