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# Source code for langchain_core.outputs.chat_generation

    from __future__ import annotations

    from typing import Any, Dict, List, Literal

    from langchain_core.messages import BaseMessage, BaseMessageChunk
    from langchain_core.outputs.generation import Generation
    from langchain_core.pydantic_v1 import root_validator
    from langchain_core.utils._merge import merge_dicts

    class ChatGeneration(Generation):
        """A single chat generation output."""

        text: str = ""
        """*SHOULD NOT BE SET DIRECTLY* The text contents of the output message."""
        message: BaseMessage
        """The message output by the chat model."""
        # Override type to be ChatGeneration, ignore mypy error as this is intentional
        type: Literal["ChatGeneration"] = "ChatGeneration"  # type: ignore[assignment]
        """Type is used exclusively for serialization purposes."""

        @root_validator
        def set_text(cls, values: Dict[str, Any]) -> Dict[str, Any]:
            """Set the text attribute to be the contents of the message."""
            try:
                text = ""
                if isinstance(values["message"].content, str):
                    text = values["message"].content
                # HACK: Assumes text in content blocks in OpenAI format.
                # Uses first text block.
                elif isinstance(values["message"].content, list):
                    for block in values["message"].content:
                        if isinstance(block, str):
                            text = block
                            break
                        elif isinstance(block, dict) and "text" in block:
                            text = block["text"]
                            break
                        else:
                            pass
                else:
                    pass
                values["text"] = text
            except (KeyError, AttributeError) as e:
                raise ValueError("Error while initializing ChatGeneration") from e
            return values

        @classmethod
        def get_lc_namespace(cls) -> List[str]:
            """Get the namespace of the langchain object."""
            return ["langchain", "schema", "output"]

    class ChatGenerationChunk(ChatGeneration):
        """ChatGeneration chunk, which can be concatenated with other
          ChatGeneration chunks.

        Attributes:
            message: The message chunk output by the chat model.
        """

        message: BaseMessageChunk
        # Override type to be ChatGeneration, ignore mypy error as this is intentional
        type: Literal["ChatGenerationChunk"] = "ChatGenerationChunk"  # type: ignore[assignment] # noqa: E501
        """Type is used exclusively for serialization purposes."""

        @classmethod
        def get_lc_namespace(cls) -> List[str]:
            """Get the namespace of the langchain object."""
            return ["langchain", "schema", "output"]

        def __add__(self, other: ChatGenerationChunk) -> ChatGenerationChunk:
            if isinstance(other, ChatGenerationChunk):
                generation_info = merge_dicts(
                    self.generation_info or {},
                    other.generation_info or {},
                )
                return ChatGenerationChunk(
                    message=self.message + other.message,
                    generation_info=generation_info or None,
                )
            else:
                raise TypeError(
                    f"unsupported operand type(s) for +: '{type(self)}' and '{type(other)}'"
                )