接口

为了尽可能简化创建自定义链的过程，我们实现了一个名为"Runnable"的协议，大多数组件都实现了该协议。这是一个标准接口，包含了一些不同的方法，可以方便地定义自定义链，并以标准方式调用它们。暴露的标准接口包括：

• stream：流式返回响应的块
• invoke：调用输入上的链
• batch：调用输入列表上的链

这些方法也有对应的异步方法：

• astream：异步流式返回响应的块
• ainvoke：异步调用输入上的链
• abatch：异步调用输入列表上的链

输入类型因组件而异：

组件	输入类型
Prompt	字典
Retriever	单个字符串
Model	单个字符串、聊天消息列表或 PromptValue

输出类型也因组件而异：

组件	输出类型
LLM	字符串
ChatModel	ChatMessage
Prompt	PromptValue
Retriever	文档列表

让我们来看看这些方法！为此，我们将创建一个非常简单的PromptTemplate + ChatModel链。

from langchain.prompts import ChatPromptTemplate  
from langchain.chat_models import ChatOpenAI  

#### API 参考:

  * [ChatPromptTemplate](https://api.python.langchain.com/en/latest/prompts/langchain.prompts.chat.ChatPromptTemplate.html) 来自 `langchain.prompts`
  * [ChatOpenAI](https://api.python.langchain.com/en/latest/chat_models/langchain.chat_models.openai.ChatOpenAI.html) 来自 `langchain.chat_models`

model = ChatOpenAI()  

prompt = ChatPromptTemplate.from_template("tell me a joke about {topic}")  

chain = prompt | model  

Stream​

for s in chain.stream({"topic": "bears"}):  
    print(s.content, end="", flush=True)  

    Sure, here's a bear-themed joke for you:  
    
    Why don't bears wear shoes?  
    
    Because they have bear feet!  

Invoke​

chain.invoke({"topic": "bears"})  

    AIMessage(content="Why don't bears wear shoes?\n\nBecause they already have bear feet!", additional_kwargs={}, example=False)  

Batch​

chain.batch([{"topic": "bears"}, {"topic": "cats"}])  

    [AIMessage(content="Why don't bears ever wear shoes?\n\nBecause they have bear feet!", additional_kwargs={}, example=False),  
     AIMessage(content="Why don't cats play poker in the wild?\n\nToo many cheetahs!", additional_kwargs={}, example=False)]  

Async Stream​

async for s in chain.astream({"topic": "bears"}):  
    print(s.content, end="", flush=True)  

    Why don't bears wear shoes?  
    
    Because they have bear feet!  

Async Invoke​

await chain.ainvoke({"topic": "bears"})  

    AIMessage(content="Sure, here you go:\n\nWhy don't bears wear shoes?\n\nBecause they have bear feet!", additional_kwargs={}, example=False)  

Async Batch​

await chain.abatch([{"topic": "bears"}])  

    [AIMessage(content="Why don't bears wear shoes?\n\nBecause they have bear feet!", additional_kwargs={}, example=False)]