add repr for not serializable (#10071)

Co-authored-by: Nuno Campos <nuno@boringbits.io>

libs/langchain/langchain/callbacks/manager.py

@@ -1193,7 +1193,6 @@ class CallbackManager(BaseCallbackManager):
         """
         if run_id is None:
             run_id = uuid.uuid4()
-
         _handle_event(
             self.handlers,
             "on_chain_start",

libs/langchain/langchain/load/serializable.py

@@ -1,5 +1,5 @@
 from abc import ABC
-from typing import Any, Dict, List, Literal, TypedDict, Union, cast
+from typing import Any, Dict, List, Literal, Optional, TypedDict, Union, cast
 
 from langchain.pydantic_v1 import BaseModel, PrivateAttr
 
@@ -28,6 +28,7 @@ class SerializedNotImplemented(BaseSerialized):
     """Serialized not implemented."""
 
     type: Literal["not_implemented"]
+    repr: Optional[str]
 
 
 class Serializable(BaseModel, ABC):
@@ -156,8 +157,15 @@ def to_json_not_implemented(obj: object) -> SerializedNotImplemented:
             _id = [*obj.__class__.__module__.split("."), obj.__class__.__name__]
     except Exception:
         pass
-    return {
+
+    result: SerializedNotImplemented = {
         "lc": 1,
         "type": "not_implemented",
         "id": _id,
+        "repr": None,
     }
+    try:
+        result["repr"] = repr(obj)
+    except Exception:
+        pass
+    return result

libs/langchain/langchain/schema/runnable/base.py

@@ -1697,6 +1697,9 @@ class RunnableLambda(Runnable[Input, Output]):
         else:
             return False
 
+    def __repr__(self) -> str:
+        return "RunnableLambda(...)"
+
     def _invoke(
         self,
         input: Input,

libs/langchain/tests/unit_tests/load/__snapshots__/test_dump.ambr

@@ -229,7 +229,8 @@
               "api_resources",
               "completion",
               "Completion"
-            ]
+            ],
+            "repr": "<class 'openai.api_resources.completion.Completion'>"
           }
         }
       },