ToolCallChunk Class — langchain Architecture

Source Code

libs/core/langchain_core/messages/content.py lines 291–333

class ToolCallChunk(TypedDict):
    """A chunk of a tool call (yielded when streaming).

    When merging `ToolCallChunks` (e.g., via `AIMessageChunk.__add__`),
    all string attributes are concatenated. Chunks are only merged if their
    values of `index` are equal and not `None`.

    Example:
    ```python
    left_chunks = [ToolCallChunk(name="foo", args='{"a":', index=0)]
    right_chunks = [ToolCallChunk(name=None, args="1}", index=0)]

    (
        AIMessageChunk(content="", tool_call_chunks=left_chunks)
        + AIMessageChunk(content="", tool_call_chunks=right_chunks)
    ).tool_call_chunks == [ToolCallChunk(name="foo", args='{"a":1}', index=0)]
    ```
    """

    # TODO: Consider making fields NotRequired[str] in the future.

    type: Literal["tool_call_chunk"]
    """Used for serialization."""

    id: str | None
    """An identifier associated with the tool call.

    An identifier is needed to associate a tool call request with a tool
    call result in events when multiple concurrent tool calls are made.
    """
    # TODO: Consider making this NotRequired[str] in the future.

    name: str | None
    """The name of the tool to be called."""

    args: str | None
    """The arguments to the tool call."""

    index: NotRequired[int | str]
    """The index of the tool call in a sequence."""

    extras: NotRequired[dict[str, Any]]
    """Provider-specific metadata."""