override() — langchain Function Reference

Source Code

libs/langchain_v1/langchain/agents/middleware/types.py lines 202–268

    def override(self, **overrides: Unpack[_ModelRequestOverrides]) -> ModelRequest[ContextT]:
        """Replace the request with a new request with the given overrides.

        Returns a new `ModelRequest` instance with the specified attributes replaced.

        This follows an immutable pattern, leaving the original request unchanged.

        Args:
            **overrides: Keyword arguments for attributes to override.

                Supported keys:

                - `model`: `BaseChatModel` instance
                - `system_prompt`: deprecated, use `system_message` instead
                - `system_message`: `SystemMessage` instance
                - `messages`: `list` of messages
                - `tool_choice`: Tool choice configuration
                - `tools`: `list` of available tools
                - `response_format`: Response format specification
                - `model_settings`: Additional model settings
                - `state`: Agent state dictionary

        Returns:
            New `ModelRequest` instance with specified overrides applied.

        Examples:
            !!! example "Create a new request with different model"

                ```python
                new_request = request.override(model=different_model)
                ```

            !!! example "Override system message (preferred)"

                ```python
                from langchain_core.messages import SystemMessage

                new_request = request.override(
                    system_message=SystemMessage(content="New instructions")
                )
                ```

            !!! example "Override multiple attributes"

                ```python
                new_request = request.override(
                    model=ChatOpenAI(model="gpt-4o"),
                    system_message=SystemMessage(content="New instructions"),
                )
                ```

        Raises:
            ValueError: If both `system_prompt` and `system_message` are provided.
        """
        # Handle system_prompt/system_message conversion
        if "system_prompt" in overrides and "system_message" in overrides:
            msg = "Cannot specify both system_prompt and system_message"
            raise ValueError(msg)

        if "system_prompt" in overrides:
            system_prompt = cast("str | None", overrides.pop("system_prompt"))  # type: ignore[typeddict-item]
            if system_prompt is None:
                overrides["system_message"] = None
            else:
                overrides["system_message"] = SystemMessage(content=system_prompt)

        return replace(self, **overrides)