langchain/docs/extras/guides/expression_language/interface.ipynb

Interface

In an effort to make it as easy as possible to create custom chains, we've implemented a "Runnable" protocol that most components implement. This is a standard interface with a few different methods, which makes it easy to define custom chains as well as making it possible to invoke them in a standard way. The standard interface exposed includes:

• stream: stream back chunks of the response
• invoke: call the chain on an input
• batch: call the chain on a list of inputs

These also have corresponding async methods:

• astream: stream back chunks of the response async
• ainvoke: call the chain on an input async
• abatch: call the chain on a list of inputs async

The type of the input varies by component:

Component	Input Type
Prompt	Dictionary
Retriever	Single string
Model	Single string, list of chat messages or a PromptValue

The output type also varies by component:

Component	Output Type
LLM	String
ChatModel	ChatMessage
Prompt	PromptValue
Retriever	List of documents

Let's take a look at these methods! To do so, we'll create a super simple PromptTemplate + ChatModel chain.

In [20]:

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

In [2]:

model = ChatOpenAI()

In [6]:

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

In [7]:

chain = prompt | model

Stream

In [8]:

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

In [9]:

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

Out [9]:

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

Batch

In [19]:

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

Out [19]:

[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

In [13]:

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

In [16]:

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

Out [16]:

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

In [18]:

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

Out [18]:

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