langchain_integration.md

Local LangChain with FastChat

LangChain is a library that facilitates the development of applications by leveraging large language models (LLMs) and enabling their composition with other sources of computation or knowledge. FastChat's OpenAI-compatible API server enables using LangChain with open models seamlessly.

Launch RESTful API Server

Here are the steps to launch a local OpenAI API server for LangChain.

First, launch the controller

python3 -m fastchat.serve.controller

Due to the fact that langchain checks whether the model's name belongs to OpenAI, we need to assign a faux OpenAI name to the Vicuna model. In essence, we're providing an OpenAI model name when loading the model. Replace /path/to/weights below with the a real path to a local model such as Vicuna. It can also be a Hugging Face repo id such as lmsys/fastchat-t5-3b-v1.0.

python3 -m fastchat.serve.model_worker --model-name 'text-embedding-ada-002' --model-path /path/to/weights

Finally, launch the RESTful API server

python3 -m fastchat.serve.openai_api_server --host localhost --port 8000

Set OpenAI Environment

You can set your environment with the following commands.

Set OpenAI base url

export OPENAI_API_BASE=http://localhost:8000/v1

Set OpenAI API key

export OPENAI_API_KEY=EMPTY

Try local LangChain

Here is a question answerting example.

from langchain.document_loaders import TextLoader
from langchain.indexes import VectorstoreIndexCreator
from langchain.embeddings import OpenAIEmbeddings
from langchain.llms import OpenAI
import openai

embedding = OpenAIEmbeddings(model="text-embedding-ada-002")
# wget https://raw.githubusercontent.com/hwchase17/langchain/master/docs/modules/state_of_the_union.txt
loader = TextLoader('state_of_the_union.txt')
index = VectorstoreIndexCreator(embedding=embedding).from_loaders([loader])

llm = OpenAI(model="text-embedding-ada-002") # select your faux openai model name
# llm = OpenAI(model="gpt-3.5-turbo")

questions = [
             "who is the speaker", 
             "What did the president say about Ketanji Brown Jackson", 
             "What are the threats to America", 
             "Who are mentioned in the speech",
             "Who is the vice president",
             "How many projects were announced",
            ]

for query in questions:
    print("Query: ", query)
    print("Ans: ",index.query(query,llm=llm))