init() — langchain Function Reference

Architecture documentation for the __init__() function in branch.py from the langchain codebase.

Function python LangChainCore Runnables

Entity Profile

LangChainCore→ Runnables→ __init__() — langchain Function Reference

Dependency Diagram

graph TD
  d857a65b_857b_e924_118a_bc4f5364cfaa["__init__()"]
  8c770be5_e4c6_a7e0_4227_c2085f2c1314["RunnableBranch"]
  d857a65b_857b_e924_118a_bc4f5364cfaa -->|defined in| 8c770be5_e4c6_a7e0_4227_c2085f2c1314
  style d857a65b_857b_e924_118a_bc4f5364cfaa fill:#6366f1,stroke:#818cf8,color:#fff

Relationship Graph

Source Code

libs/core/langchain_core/runnables/branch.py lines 74–137

    def __init__(
        self,
        *branches: tuple[
            Runnable[Input, bool]
            | Callable[[Input], bool]
            | Callable[[Input], Awaitable[bool]],
            RunnableLike,
        ]
        | RunnableLike,
    ) -> None:
        """A `Runnable` that runs one of two branches based on a condition.

        Args:
            *branches: A list of `(condition, Runnable)` pairs.
                Defaults a `Runnable` to run if no condition is met.

        Raises:
            ValueError: If the number of branches is less than `2`.
            TypeError: If the default branch is not `Runnable`, `Callable` or `Mapping`.
            TypeError: If a branch is not a `tuple` or `list`.
            ValueError: If a branch is not of length `2`.
        """
        if len(branches) < _MIN_BRANCHES:
            msg = "RunnableBranch requires at least two branches"
            raise ValueError(msg)

        default = branches[-1]

        if not isinstance(
            default,
            (Runnable, Callable, Mapping),  # type: ignore[arg-type]
        ):
            msg = "RunnableBranch default must be Runnable, callable or mapping."
            raise TypeError(msg)

        default_ = cast(
            "Runnable[Input, Output]", coerce_to_runnable(cast("RunnableLike", default))
        )

        branches_ = []

        for branch in branches[:-1]:
            if not isinstance(branch, (tuple, list)):
                msg = (
                    f"RunnableBranch branches must be "
                    f"tuples or lists, not {type(branch)}"
                )
                raise TypeError(msg)

            if len(branch) != _MIN_BRANCHES:
                msg = (
                    f"RunnableBranch branches must be "
                    f"tuples or lists of length 2, not {len(branch)}"
                )
                raise ValueError(msg)
            condition, runnable = branch
            condition = cast("Runnable[Input, bool]", coerce_to_runnable(condition))
            runnable = coerce_to_runnable(runnable)
            branches_.append((condition, runnable))

        super().__init__(
            branches=branches_,
            default=default_,
        )