core[patch]: handle serializable fields that cant be converted to bool (#25903)

libs/core/langchain_core/load/serializable.py

@@ -262,7 +262,27 @@ def _is_field_useful(inst: Serializable, key: str, value: Any) -> bool:
     field = inst.__fields__.get(key)
     if not field:
         return False
-    return field.required is True or value or field.get_default() != value
+    # Handle edge case: a value cannot be converted to a boolean (e.g. a
+    # Pandas DataFrame).
+    try:
+        value_is_truthy = bool(value)
+    except Exception as _:
+        value_is_truthy = 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
+
+    return field.required is True or value_is_truthy or value_neq_default
 
 
 def _replace_secrets(

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

@@ -1,6 +1,8 @@
 from typing import Dict
 
 from langchain_core.load import Serializable, dumpd
+from langchain_core.load.serializable import _is_field_useful
+from langchain_core.pydantic_v1 import Field
 
 
 def test_simple_serialization() -> None:
@@ -69,3 +71,39 @@ def test_simple_serialization_secret() -> None:
         "lc": 1,
         "type": "constructor",
     }
+
+
+def test__is_field_useful() -> None:
+    class ArrayObj:
+        def __bool__(self) -> bool:
+            raise ValueError("Truthiness can't be determined")
+
+        def __eq__(self, other: object) -> bool:
+            return self  # type: ignore[return-value]
+
+    class NonBoolObj:
+        def __bool__(self) -> bool:
+            raise ValueError("Truthiness can't be determined")
+
+        def __eq__(self, other: object) -> bool:
+            raise ValueError("Equality can't be determined")
+
+    default_x = ArrayObj()
+    default_y = NonBoolObj()
+
+    class Foo(Serializable):
+        x: ArrayObj = Field(default=default_x)
+        y: NonBoolObj = Field(default=default_y)
+        # Make sure works for fields without default.
+        z: ArrayObj
+
+        class Config:
+            arbitrary_types_allowed = True
+
+    foo = Foo(x=ArrayObj(), y=NonBoolObj(), z=ArrayObj())
+    assert _is_field_useful(foo, "x", foo.x)
+    assert _is_field_useful(foo, "y", foo.y)
+
+    foo = Foo(x=default_x, y=default_y, z=ArrayObj())
+    assert not _is_field_useful(foo, "x", foo.x)
+    assert not _is_field_useful(foo, "y", foo.y)