langchain/libs/community/langchain_community/chat_models/litellm_router.py

"""LiteLLM Router as LangChain Model."""
from typing import (
    Any,
    AsyncIterator,
    Iterator,
    List,
    Mapping,
    Optional,
)

from langchain_core.callbacks.manager import (
    AsyncCallbackManagerForLLMRun,
    CallbackManagerForLLMRun,
)
from langchain_core.language_models.chat_models import (
    agenerate_from_stream,
    generate_from_stream,
)
from langchain_core.messages import (
    AIMessageChunk,
    BaseMessage,
)
from langchain_core.outputs import (
    ChatGeneration,
    ChatGenerationChunk,
    ChatResult,
)

from langchain_community.chat_models.litellm import (
    ChatLiteLLM,
    _convert_delta_to_message_chunk,
    _convert_dict_to_message,
)

token_usage_key_name = "token_usage"
model_extra_key_name = "model_extra"


def get_llm_output(usage: Any, **params: Any) -> dict:
    """Get llm output from usage and params."""
    llm_output = {token_usage_key_name: usage}
    # copy over metadata (metadata came from router completion call)
    metadata = params["metadata"]
    for key in metadata:
        if key not in llm_output:
            # if token usage in metadata, prefer metadata's copy of it
            llm_output[key] = metadata[key]
    return llm_output


class ChatLiteLLMRouter(ChatLiteLLM):
    """LiteLLM Router as LangChain Model."""

    router: Any

    def __init__(self, *, router: Any, **kwargs: Any) -> None:
        """Construct Chat LiteLLM Router."""
        super().__init__(**kwargs)
        self.router = router

    @property
    def _llm_type(self) -> str:
        return "LiteLLMRouter"

    def _set_model_for_completion(self) -> None:
        # use first model name (aka: model group),
        # since we can only pass one to the router completion functions
        self.model = self.router.model_list[0]["model_name"]

    def _prepare_params_for_router(self, params: Any) -> None:
        params["model"] = self.model

        # allow the router to set api_base based on its model choice
        api_base_key_name = "api_base"
        if api_base_key_name in params and params[api_base_key_name] is None:
            del params[api_base_key_name]

        # add metadata so router can fill it below
        params.setdefault("metadata", {})

    def _generate(
        self,
        messages: List[BaseMessage],
        stop: Optional[List[str]] = None,
        run_manager: Optional[CallbackManagerForLLMRun] = None,
        stream: Optional[bool] = None,
        **kwargs: Any,
    ) -> ChatResult:
        should_stream = stream if stream is not None else self.streaming
        if should_stream:
            stream_iter = self._stream(
                messages, stop=stop, run_manager=run_manager, **kwargs
            )
            return generate_from_stream(stream_iter)

        message_dicts, params = self._create_message_dicts(messages, stop)
        params = {**params, **kwargs}
        self._set_model_for_completion()
        self._prepare_params_for_router(params)

        response = self.router.completion(
            messages=message_dicts,
            **params,
        )
        return self._create_chat_result(response, **params)

    def _stream(
        self,
        messages: List[BaseMessage],
        stop: Optional[List[str]] = None,
        run_manager: Optional[CallbackManagerForLLMRun] = None,
        **kwargs: Any,
    ) -> Iterator[ChatGenerationChunk]:
        default_chunk_class = AIMessageChunk
        message_dicts, params = self._create_message_dicts(messages, stop)
        params = {**params, **kwargs, "stream": True}
        self._set_model_for_completion()
        self._prepare_params_for_router(params)

        for chunk in self.router.completion(messages=message_dicts, **params):
            if len(chunk["choices"]) == 0:
                continue
            delta = chunk["choices"][0]["delta"]
            chunk = _convert_delta_to_message_chunk(delta, default_chunk_class)
            default_chunk_class = chunk.__class__
            yield ChatGenerationChunk(message=chunk)
            if run_manager:
                run_manager.on_llm_new_token(chunk.content, **params)

    async def _astream(
        self,
        messages: List[BaseMessage],
        stop: Optional[List[str]] = None,
        run_manager: Optional[AsyncCallbackManagerForLLMRun] = None,
        **kwargs: Any,
    ) -> AsyncIterator[ChatGenerationChunk]:
        default_chunk_class = AIMessageChunk
        message_dicts, params = self._create_message_dicts(messages, stop)
        params = {**params, **kwargs, "stream": True}
        self._set_model_for_completion()
        self._prepare_params_for_router(params)

        async for chunk in await self.router.acompletion(
            messages=message_dicts, **params
        ):
            if len(chunk["choices"]) == 0:
                continue
            delta = chunk["choices"][0]["delta"]
            chunk = _convert_delta_to_message_chunk(delta, default_chunk_class)
            default_chunk_class = chunk.__class__
            yield ChatGenerationChunk(message=chunk)
            if run_manager:
                await run_manager.on_llm_new_token(chunk.content, **params)

    async def _agenerate(
        self,
        messages: List[BaseMessage],
        stop: Optional[List[str]] = None,
        run_manager: Optional[AsyncCallbackManagerForLLMRun] = None,
        stream: Optional[bool] = None,
        **kwargs: Any,
    ) -> ChatResult:
        should_stream = stream if stream is not None else self.streaming
        if should_stream:
            stream_iter = self._astream(
                messages=messages, stop=stop, run_manager=run_manager, **kwargs
            )
            return await agenerate_from_stream(stream_iter)

        message_dicts, params = self._create_message_dicts(messages, stop)
        params = {**params, **kwargs}
        self._set_model_for_completion()
        self._prepare_params_for_router(params)

        response = await self.router.acompletion(
            messages=message_dicts,
            **params,
        )
        return self._create_chat_result(response, **params)

    # from
    # https://github.com/langchain-ai/langchain/blob/master/libs/community/langchain_community/chat_models/openai.py
    # but modified to handle LiteLLM Usage class
    def _combine_llm_outputs(self, llm_outputs: List[Optional[dict]]) -> dict:
        overall_token_usage: dict = {}
        system_fingerprint = None
        for output in llm_outputs:
            if output is None:
                # Happens in streaming
                continue
            token_usage = output["token_usage"]
            if token_usage is not None:
                # get dict from LiteLLM Usage class
                for k, v in token_usage.dict().items():
                    if k in overall_token_usage:
                        overall_token_usage[k] += v
                    else:
                        overall_token_usage[k] = v
            if system_fingerprint is None:
                system_fingerprint = output.get("system_fingerprint")
        combined = {"token_usage": overall_token_usage, "model_name": self.model_name}
        if system_fingerprint:
            combined["system_fingerprint"] = system_fingerprint
        return combined

    def _create_chat_result(
        self, response: Mapping[str, Any], **params: Any
    ) -> ChatResult:
        from litellm.utils import Usage

        generations = []
        for res in response["choices"]:
            message = _convert_dict_to_message(res["message"])
            gen = ChatGeneration(
                message=message,
                generation_info=dict(finish_reason=res.get("finish_reason")),
            )
            generations.append(gen)
        token_usage = response.get("usage", Usage(prompt_tokens=0, total_tokens=0))
        llm_output = get_llm_output(token_usage, **params)
        return ChatResult(generations=generations, llm_output=llm_output)