core[patch]: fix repr and str for Serializable (#26786)

Fixes #26499

---------

Co-authored-by: Bagatur <22008038+baskaryan@users.noreply.github.com>

libs/core/langchain_core/load/serializable.py

@@ -10,6 +10,7 @@ from typing import (
 )
 
 from pydantic import BaseModel, ConfigDict
+from pydantic.fields import FieldInfo
 from typing_extensions import NotRequired
 
 
@@ -77,10 +78,23 @@ def try_neq_default(value: Any, key: str, model: BaseModel) -> bool:
     Raises:
         Exception: If the key is not in the model.
     """
+    field = model.model_fields[key]
+    return _try_neq_default(value, field)
+
+
+def _try_neq_default(value: Any, field: FieldInfo) -> bool:
+    # Handle edge case: inequality of two objects does not evaluate to a bool (e.g. two
+    # Pandas DataFrames).
     try:
-        return model.model_fields[key].get_default() != value
-    except Exception:
-        return True
+        return bool(field.get_default() != value)
+    except Exception as _:
+        try:
+            return all(field.get_default() != value)
+        except Exception as _:
+            try:
+                return value is not field.default
+            except Exception as _:
+                return False
 
 
 class Serializable(BaseModel, ABC):
@@ -297,18 +311,7 @@ def _is_field_useful(inst: Serializable, key: str, value: Any) -> bool:
     if field.default_factory is list and isinstance(value, list):
         return False
 
-    # Handle edge case: inequality of two objects does not evaluate to a bool (e.g. two
-    # Pandas DataFrames).
-    try:
-        value_neq_default = bool(field.get_default() != value)
-    except Exception as _:
-        try:
-            value_neq_default = all(field.get_default() != value)
-        except Exception as _:
-            try:
-                value_neq_default = value is not field.default
-            except Exception as _:
-                value_neq_default = False
+    value_neq_default = _try_neq_default(value, field)
 
     # If value is falsy and does not match the default
     return value_is_truthy or value_neq_default

libs/core/tests/unit_tests/load/test_serializable.py

@@ -4,6 +4,22 @@ from langchain_core.load import Serializable, dumpd, load
 from langchain_core.load.serializable import _is_field_useful
 
 
+class NonBoolObj:
+    def __bool__(self) -> bool:
+        msg = "Truthiness can't be determined"
+        raise ValueError(msg)
+
+    def __eq__(self, other: object) -> bool:
+        msg = "Equality can't be determined"
+        raise ValueError(msg)
+
+    def __str__(self) -> str:
+        return self.__class__.__name__
+
+    def __repr__(self) -> str:
+        return self.__class__.__name__
+
+
 def test_simple_serialization() -> None:
     class Foo(Serializable):
         bar: int
@@ -82,15 +98,6 @@ def test__is_field_useful() -> None:
         def __eq__(self, other: object) -> bool:
             return self  # type: ignore[return-value]
 
-    class NonBoolObj:
-        def __bool__(self) -> bool:
-            msg = "Truthiness can't be determined"
-            raise ValueError(msg)
-
-        def __eq__(self, other: object) -> bool:
-            msg = "Equality can't be determined"
-            raise ValueError(msg)
-
     default_x = ArrayObj()
     default_y = NonBoolObj()
 
@@ -169,3 +176,30 @@ def test_simple_deserialization_with_additional_imports() -> None:
         },
     )
     assert isinstance(new_foo, Foo2)
+
+
+class Foo3(Serializable):
+    model_config = ConfigDict(arbitrary_types_allowed=True)
+
+    content: str
+    non_bool: NonBoolObj
+
+    @classmethod
+    def is_lc_serializable(cls) -> bool:
+        return True
+
+
+def test_repr() -> None:
+    foo = Foo3(
+        content="repr",
+        non_bool=NonBoolObj(),
+    )
+    assert repr(foo) == "Foo3(content='repr', non_bool=NonBoolObj)"
+
+
+def test_str() -> None:
+    foo = Foo3(
+        content="str",
+        non_bool=NonBoolObj(),
+    )
+    assert str(foo) == "content='str' non_bool=NonBoolObj"