Source code for langchain.prompts.chat
"""Chat prompt template."""
from __future__ import annotations
from abc import ABC, abstractmethod
from pathlib import Path
from typing import Any, Callable, List, Sequence, Tuple, Type, TypeVar, Union
from pydantic import Field
from langchain.load.serializable import Serializable
from langchain.memory.buffer import get_buffer_string
from langchain.prompts.base import BasePromptTemplate, StringPromptTemplate
from langchain.prompts.prompt import PromptTemplate
from langchain.schema import (
    AIMessage,
    BaseMessage,
    ChatMessage,
    HumanMessage,
    PromptValue,
    SystemMessage,
)
class BaseMessagePromptTemplate(Serializable, ABC):
    @property
    def lc_serializable(self) -> bool:
        return True
    @abstractmethod
    def format_messages(self, **kwargs: Any) -> List[BaseMessage]:
        """To messages."""
    @property
    @abstractmethod
    def input_variables(self) -> List[str]:
        """Input variables for this prompt template."""
[docs]class MessagesPlaceholder(BaseMessagePromptTemplate):
    """Prompt template that assumes variable is already list of messages."""
    variable_name: str
[docs]    def format_messages(self, **kwargs: Any) -> List[BaseMessage]:
        """To a BaseMessage."""
        value = kwargs[self.variable_name]
        if not isinstance(value, list):
            raise ValueError(
                f"variable {self.variable_name} should be a list of base messages, "
                f"got {value}"
            )
        for v in value:
            if not isinstance(v, BaseMessage):
                raise ValueError(
                    f"variable {self.variable_name} should be a list of base messages,"
                    f" got {value}"
                )
rtdocs_stable/api.python.langchain.com/en/stable/_modules/langchain/prompts/chat.html