RunnableConfigurableAlternatives Class — langchain Architecture

Source Code

libs/core/langchain_core/runnables/configurable.py lines 475–638

class RunnableConfigurableAlternatives(DynamicRunnable[Input, Output]):
    """`Runnable` that can be dynamically configured.

    A `RunnableConfigurableAlternatives` should be initiated using the
    `configurable_alternatives` method of a `Runnable` or can be
    initiated directly as well.

    Here is an example of using a `RunnableConfigurableAlternatives` that uses
    alternative prompts to illustrate its functionality:

        ```python
        from langchain_core.runnables import ConfigurableField
        from langchain_openai import ChatOpenAI

        # This creates a RunnableConfigurableAlternatives for Prompt Runnable
        # with two alternatives.
        prompt = PromptTemplate.from_template(
            "Tell me a joke about {topic}"
        ).configurable_alternatives(
            ConfigurableField(id="prompt"),
            default_key="joke",
            poem=PromptTemplate.from_template("Write a short poem about {topic}"),
        )

        # When invoking the created RunnableSequence, you can pass in the
        # value for your ConfigurableField's id which in this case will either be
        # `joke` or `poem`.
        chain = prompt | ChatOpenAI(model="gpt-3.5-turbo-0125", temperature=0)

        # The `with_config` method brings in the desired Prompt Runnable in your
        # Runnable Sequence.
        chain.with_config(configurable={"prompt": "poem"}).invoke({"topic": "bears"})
        ```

    Equivalently, you can initialize `RunnableConfigurableAlternatives` directly
    and use in LCEL in the same way:

        ```python
        from langchain_core.runnables import ConfigurableField
        from langchain_core.runnables.configurable import (
            RunnableConfigurableAlternatives,
        )
        from langchain_openai import ChatOpenAI

        prompt = RunnableConfigurableAlternatives(
            which=ConfigurableField(id="prompt"),
            default=PromptTemplate.from_template("Tell me a joke about {topic}"),
            default_key="joke",
            prefix_keys=False,
            alternatives={
                "poem": PromptTemplate.from_template("Write a short poem about {topic}")
            },
        )
        chain = prompt | ChatOpenAI(model="gpt-3.5-turbo-0125", temperature=0)
        chain.with_config(configurable={"prompt": "poem"}).invoke({"topic": "bears"})
        ```
    """

    which: ConfigurableField
    """The `ConfigurableField` to use to choose between alternatives."""

    alternatives: dict[
        str,
        Runnable[Input, Output] | Callable[[], Runnable[Input, Output]],
    ]
    """The alternatives to choose from."""

    default_key: str = "default"
    """The enum value to use for the default option."""

    prefix_keys: bool
    """Whether to prefix configurable fields of each alternative with a namespace
    of the form <which.id>==<alternative_key>, e.g. a key named "temperature" used by
    the alternative named "gpt3" becomes "model==gpt3/temperature".
    """

    @property
    @override
    def config_specs(self) -> list[ConfigurableFieldSpec]:
        with _enums_for_spec_lock:
            if which_enum := _enums_for_spec.get(self.which):