StdOutCallbackHandler Class — langchain Architecture

Architecture documentation for the StdOutCallbackHandler class in stdout.py from the langchain codebase.

Class python

Entity Profile

Dependency Diagram

graph TD
  dcf2a9b2_8ab4_fbe0_5f57_ef548417d10e["StdOutCallbackHandler"]
  af283d05_75a6_5813_267b_f03a32501460["BaseCallbackHandler"]
  dcf2a9b2_8ab4_fbe0_5f57_ef548417d10e -->|extends| af283d05_75a6_5813_267b_f03a32501460
  0ac81bdf_4e75_0bc6_a08b_3f201a8e9da1["stdout.py"]
  dcf2a9b2_8ab4_fbe0_5f57_ef548417d10e -->|defined in| 0ac81bdf_4e75_0bc6_a08b_3f201a8e9da1
  706efa82_e825_167a_0237_a721f8185def["__init__()"]
  dcf2a9b2_8ab4_fbe0_5f57_ef548417d10e -->|method| 706efa82_e825_167a_0237_a721f8185def
  8245925b_379e_91d8_182e_d404bc9515ee["on_chain_start()"]
  dcf2a9b2_8ab4_fbe0_5f57_ef548417d10e -->|method| 8245925b_379e_91d8_182e_d404bc9515ee
  d49bad0e_757b_b92c_a5da_4c3d949372f3["on_chain_end()"]
  dcf2a9b2_8ab4_fbe0_5f57_ef548417d10e -->|method| d49bad0e_757b_b92c_a5da_4c3d949372f3
  6d45cae6_dc82_8565_0075_94e95353b674["on_agent_action()"]
  dcf2a9b2_8ab4_fbe0_5f57_ef548417d10e -->|method| 6d45cae6_dc82_8565_0075_94e95353b674
  9b871232_001e_2f5e_a2c6_e390b77ed440["on_tool_end()"]
  dcf2a9b2_8ab4_fbe0_5f57_ef548417d10e -->|method| 9b871232_001e_2f5e_a2c6_e390b77ed440
  c011477e_678b_fe9a_e5b4_f9b294075a13["on_text()"]
  dcf2a9b2_8ab4_fbe0_5f57_ef548417d10e -->|method| c011477e_678b_fe9a_e5b4_f9b294075a13
  515de6a0_4d8b_67cc_455a_065218e2e8c7["on_agent_finish()"]
  dcf2a9b2_8ab4_fbe0_5f57_ef548417d10e -->|method| 515de6a0_4d8b_67cc_455a_065218e2e8c7

Relationship Graph

Source Code

libs/core/langchain_core/callbacks/stdout.py lines 16–123

class StdOutCallbackHandler(BaseCallbackHandler):
    """Callback handler that prints to std out."""

    def __init__(self, color: str | None = None) -> None:
        """Initialize callback handler.

        Args:
            color: The color to use for the text.
        """
        self.color = color

    @override
    def on_chain_start(
        self, serialized: dict[str, Any], inputs: dict[str, Any], **kwargs: Any
    ) -> None:
        """Print out that we are entering a chain.

        Args:
            serialized: The serialized chain.
            inputs: The inputs to the chain.
            **kwargs: Additional keyword arguments.
        """
        if "name" in kwargs:
            name = kwargs["name"]
        elif serialized:
            name = serialized.get("name", serialized.get("id", ["<unknown>"])[-1])
        else:
            name = "<unknown>"
        print(f"\n\n\033[1m> Entering new {name} chain...\033[0m")  # noqa: T201

    @override
    def on_chain_end(self, outputs: dict[str, Any], **kwargs: Any) -> None:
        """Print out that we finished a chain.

        Args:
            outputs: The outputs of the chain.
            **kwargs: Additional keyword arguments.
        """
        print("\n\033[1m> Finished chain.\033[0m")  # noqa: T201

    @override
    def on_agent_action(
        self, action: AgentAction, color: str | None = None, **kwargs: Any
    ) -> Any:
        """Run on agent action.

        Args:
            action: The agent action.
            color: The color to use for the text.
            **kwargs: Additional keyword arguments.
        """
        print_text(action.log, color=color or self.color)

    @override
    def on_tool_end(
        self,
        output: Any,
        color: str | None = None,
        observation_prefix: str | None = None,
        llm_prefix: str | None = None,
        **kwargs: Any,
    ) -> None:
        """If not the final action, print out observation.

        Args:
            output: The output to print.
            color: The color to use for the text.
            observation_prefix: The observation prefix.
            llm_prefix: The LLM prefix.
            **kwargs: Additional keyword arguments.
        """
        output = str(output)
        if observation_prefix is not None:
            print_text(f"\n{observation_prefix}")
        print_text(output, color=color or self.color)
        if llm_prefix is not None:
            print_text(f"\n{llm_prefix}")

    @override
    def on_text(
        self,