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libs/core/langchain_core/utils/_pydantic_adapters.py

@@ -0,0 +1,34 @@
+"""Internal adapters for migrating from pydantic v1 to v2."""
+from typing import Any, List, Sequence, Type
+
+from langchain_core.pydantic_v1 import BaseModel
+
+
+def get_model_defaults(
+    model_class: Type[BaseModel], fields: Sequence[str]
+) -> List[Any]:
+    """Get model defaults for the given fields.
+
+    Args:
+        model_class: The model class.
+        fields: The fields to get defaults for.
+
+    Returns:
+        The defaults for the given fields.
+
+        Only supports default literals right now
+    """
+    values = []
+    for field in fields:
+        model_field = model_class.__fields__[field]
+        if model_field.required:
+            raise KeyError(f"Field {field} is required")
+
+        default_value = model_class.__fields__[field].default
+
+        if not isinstance(default_value, (int, float, str, bool, type(None))):
+            raise NotImplementedError("Only literals are supported for now")
+
+        values.append(default_value)
+
+    return values

libs/core/tests/unit_tests/utils/test_pydantic_adapters.py

@@ -0,0 +1,46 @@
+"""Internal adapters for migrating from pydantic v1 to v2."""
+from typing import Any
+
+import pytest
+
+from langchain_core.pydantic_v1 import BaseModel, Field
+from langchain_core.utils._pydantic_adapters import get_model_defaults
+
+
+class MyModel(BaseModel):
+    field_with_default_int: int = Field(10)
+    field_with_default_str: str = Field("default")
+    field_with_default_none: Any = Field(None)
+    field_without_default: float
+    field_with_default_bool: bool = Field(True)
+
+
+def test_get_model_defaults():
+    # Test case 1: Get defaults for all fields with defaults
+    model_class = MyModel
+    fields = [
+        "field_with_default_int",
+        "field_with_default_str",
+        "field_with_default_none",
+        "field_with_default_bool",
+    ]
+    expected_defaults = [10, "default", None, True]
+    assert get_model_defaults(model_class, fields) == expected_defaults
+
+    # Test case 2: Get defaults for a subset of fields
+    fields = ["field_with_default_str", "field_with_default_none"]
+    expected_defaults = ["default", None]
+    assert get_model_defaults(model_class, fields) == expected_defaults
+
+    # Test case 3: Field without default should raise an AttributeError
+    fields = ["field_without_default"]
+    with pytest.raises(KeyError):
+        get_model_defaults(model_class, fields)
+
+    # Test case 4: Field with non-literal default value should raise NotImplementedError
+    class TestModelWithNonLiteralDefault(BaseModel):
+        field_with_non_literal_default: Any = Field([1, 2, 3])
+
+    fields = ["field_with_non_literal_default"]
+    with pytest.raises(NotImplementedError):
+        get_model_defaults(TestModelWithNonLiteralDefault, fields)