pick() — langchain Function Reference

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

Function python LangChainCore Runnables

Entity Profile

LangChainCore→ Runnables→ pick() — langchain Function Reference

Dependency Diagram

graph TD
  1ddfbd86_717b_2bb0_35ab_c2089cae789b["pick()"]
  4a62481c_02cb_a5de_1833_50669d5351a6["Runnable"]
  1ddfbd86_717b_2bb0_35ab_c2089cae789b -->|defined in| 4a62481c_02cb_a5de_1833_50669d5351a6
  style 1ddfbd86_717b_2bb0_35ab_c2089cae789b fill:#6366f1,stroke:#818cf8,color:#fff

Relationship Graph

Source Code

libs/core/langchain_core/runnables/base.py lines 709–770

    def pick(self, keys: str | list[str]) -> RunnableSerializable[Any, Any]:
        """Pick keys from the output `dict` of this `Runnable`.

        !!! example "Pick a single key"

            ```python
            import json

            from langchain_core.runnables import RunnableLambda, RunnableMap

            as_str = RunnableLambda(str)
            as_json = RunnableLambda(json.loads)
            chain = RunnableMap(str=as_str, json=as_json)

            chain.invoke("[1, 2, 3]")
            # -> {"str": "[1, 2, 3]", "json": [1, 2, 3]}

            json_only_chain = chain.pick("json")
            json_only_chain.invoke("[1, 2, 3]")
            # -> [1, 2, 3]
            ```

        !!! example "Pick a list of keys"

            ```python
            from typing import Any

            import json

            from langchain_core.runnables import RunnableLambda, RunnableMap

            as_str = RunnableLambda(str)
            as_json = RunnableLambda(json.loads)


            def as_bytes(x: Any) -> bytes:
                return bytes(x, "utf-8")


            chain = RunnableMap(
                str=as_str, json=as_json, bytes=RunnableLambda(as_bytes)
            )

            chain.invoke("[1, 2, 3]")
            # -> {"str": "[1, 2, 3]", "json": [1, 2, 3], "bytes": b"[1, 2, 3]"}

            json_and_bytes_chain = chain.pick(["json", "bytes"])
            json_and_bytes_chain.invoke("[1, 2, 3]")
            # -> {"json": [1, 2, 3], "bytes": b"[1, 2, 3]"}
            ```

        Args:
            keys: A key or list of keys to pick from the output dict.

        Returns:
            a new `Runnable`.

        """
        # Import locally to prevent circular import
        from langchain_core.runnables.passthrough import RunnablePick  # noqa: PLC0415

        return self | RunnablePick(keys)