langchain/libs/core/langchain_core/messages/tool.py

from typing import Any, List, Literal

from langchain_core.messages.base import (
    BaseMessage,
    BaseMessageChunk,
    merge_content,
)


class ToolMessage(BaseMessage):
    """A Message for passing the result of executing a tool back to a model."""

    tool_call_id: str
    """Tool call that this message is responding to."""

    type: Literal["tool"] = "tool"

    @classmethod
    def get_lc_namespace(cls) -> List[str]:
        """Get the namespace of the langchain object."""
        return ["langchain", "schema", "messages"]


ToolMessage.update_forward_refs()


class ToolMessageChunk(ToolMessage, BaseMessageChunk):
    """A Tool Message chunk."""

    # Ignoring mypy re-assignment here since we're overriding the value
    # to make sure that the chunk variant can be discriminated from the
    # non-chunk variant.
    type: Literal["ToolMessageChunk"] = "ToolMessageChunk"  # type: ignore[assignment]

    @classmethod
    def get_lc_namespace(cls) -> List[str]:
        """Get the namespace of the langchain object."""
        return ["langchain", "schema", "messages"]

    def __add__(self, other: Any) -> BaseMessageChunk:  # type: ignore
        if isinstance(other, ToolMessageChunk):
            if self.tool_call_id != other.tool_call_id:
                raise ValueError(
                    "Cannot concatenate ToolMessageChunks with different names."
                )

            return self.__class__(
                tool_call_id=self.tool_call_id,
                content=merge_content(self.content, other.content),
                additional_kwargs=self._merge_kwargs_dict(
                    self.additional_kwargs, other.additional_kwargs
                ),
            )

        return super().__add__(other)