__init_subclass__() — langchain Function Reference

Architecture documentation for the __init_subclass__() function in base.py from the langchain codebase.

Function python AgentOrchestration ToolInterface

Entity Profile

AgentOrchestration→ ToolInterface→ __init_subclass__() — langchain Function Reference

Dependency Diagram

graph TD
  89ef8934_385e_99ca_6def_16de079c0578["__init_subclass__()"]
  5ebe56ae_0ac8_cb13_b5a9_ee567b924009["BaseTool"]
  89ef8934_385e_99ca_6def_16de079c0578 -->|defined in| 5ebe56ae_0ac8_cb13_b5a9_ee567b924009
  style 89ef8934_385e_99ca_6def_16de079c0578 fill:#6366f1,stroke:#818cf8,color:#fff

Relationship Graph

Source Code

libs/core/langchain_core/tools/base.py lines 413–444

    def __init_subclass__(cls, **kwargs: Any) -> None:
        """Validate the tool class definition during subclass creation.

        Args:
            **kwargs: Additional keyword arguments passed to the parent class.

        Raises:
            SchemaAnnotationError: If `args_schema` has incorrect type annotation.
        """
        super().__init_subclass__(**kwargs)

        args_schema_type = cls.__annotations__.get("args_schema", None)

        if args_schema_type is not None and args_schema_type == BaseModel:
            # Throw errors for common mis-annotations.
            # TODO: Use get_args / get_origin and fully
            # specify valid annotations.
            typehint_mandate = """
class ChildTool(BaseTool):
    ...
    args_schema: Type[BaseModel] = SchemaClass
    ..."""
            name = cls.__name__
            msg = (
                f"Tool definition for {name} must include valid type annotations"
                f" for argument 'args_schema' to behave as expected.\n"
                f"Expected annotation of 'Type[BaseModel]'"
                f" but got '{args_schema_type}'.\n"
                f"Expected class looks like:\n"
                f"{typehint_mandate}"
            )
            raise SchemaAnnotationError(msg)