__init__.py — langchain Source File

Source Code

"""Core language model abstractions.

LangChain has two main classes to work with language models: chat models and
"old-fashioned" LLMs (string-in, string-out).

**Chat models**

Language models that use a sequence of messages as inputs and return chat messages
as outputs (as opposed to using plain text).

Chat models support the assignment of distinct roles to conversation messages, helping
to distinguish messages from the AI, users, and instructions such as system messages.

The key abstraction for chat models is
[`BaseChatModel`][langchain_core.language_models.BaseChatModel]. Implementations should
inherit from this class.

See existing [chat model integrations](https://docs.langchain.com/oss/python/integrations/chat).

**LLMs (legacy)**

Language models that takes a string as input and returns a string.

These are traditionally older models (newer models generally are chat models).

Although the underlying models are string in, string out, the LangChain wrappers also
allow these models to take messages as input. This gives them the same interface as
chat models. When messages are passed in as input, they will be formatted into a string
under the hood before being passed to the underlying model.
"""

from typing import TYPE_CHECKING

from langchain_core._import_utils import import_attr
from langchain_core.language_models._utils import is_openai_data_block

if TYPE_CHECKING:
    from langchain_core.language_models.base import (
        BaseLanguageModel,
        LangSmithParams,
        LanguageModelInput,
        LanguageModelLike,
        LanguageModelOutput,
        get_tokenizer,
    )
    from langchain_core.language_models.chat_models import (
        BaseChatModel,
        SimpleChatModel,
    )
    from langchain_core.language_models.fake import FakeListLLM, FakeStreamingListLLM
    from langchain_core.language_models.fake_chat_models import (
        FakeListChatModel,
        FakeMessagesListChatModel,
        GenericFakeChatModel,
        ParrotFakeChatModel,
    )
    from langchain_core.language_models.llms import LLM, BaseLLM
    from langchain_core.language_models.model_profile import (
        ModelProfile,
        ModelProfileRegistry,
    )

__all__ = (
    "LLM",
    "BaseChatModel",
    "BaseLLM",
    "BaseLanguageModel",
    "FakeListChatModel",
    "FakeListLLM",
    "FakeMessagesListChatModel",
    "FakeStreamingListLLM",
    "GenericFakeChatModel",
    "LangSmithParams",
    "LanguageModelInput",
    "LanguageModelLike",
    "LanguageModelOutput",
    "ModelProfile",
    "ModelProfileRegistry",
    "ParrotFakeChatModel",
    "SimpleChatModel",
    "get_tokenizer",
    "is_openai_data_block",
)

_dynamic_imports = {
    "BaseLanguageModel": "base",
    "LangSmithParams": "base",
    "LanguageModelInput": "base",
    "LanguageModelLike": "base",
    "LanguageModelOutput": "base",
    "get_tokenizer": "base",
    "BaseChatModel": "chat_models",
    "SimpleChatModel": "chat_models",
    "FakeListLLM": "fake",
    "FakeStreamingListLLM": "fake",
    "FakeListChatModel": "fake_chat_models",
    "FakeMessagesListChatModel": "fake_chat_models",
    "GenericFakeChatModel": "fake_chat_models",
    "ParrotFakeChatModel": "fake_chat_models",
    "LLM": "llms",
    "ModelProfile": "model_profile",
    "ModelProfileRegistry": "model_profile",
    "BaseLLM": "llms",
    "is_openai_data_block": "_utils",
}


def __getattr__(attr_name: str) -> object:
    module_name = _dynamic_imports.get(attr_name)
    result = import_attr(attr_name, module_name, __spec__.parent)
    globals()[attr_name] = result
    return result


def __dir__() -> list[str]:
    return list(__all__)