Set up LangChain

Install LangChain

To install the LangChain Python library, run the following command in your terminal or command line:

pip install langchain

To use OpenAI with LangChain, install the OpenAI Python library that integrates with LangChain:

pip install langchain-openai

Set up OpenAI API key with LangChain

Create a Python script with the following code to run your first LangChain program:

from langchain_openai import ChatOpenAI
from dotenv import load_dotenv
import os

load_dotenv('.env')

llm = ChatOpenAI(openai_api_key=os.environ.get("OPENAI_API_KEY"))

llm.invoke("how can langsmith help with testing?")

Create a chain

from langchain_openai import ChatOpenAI
from langchain_core.prompts import ChatPromptTemplate
from langchain_core.output_parsers import StrOutputParser
from dotenv import load_dotenv
import os

load_dotenv('.env')

llm = ChatOpenAI(openai_api_key=os.environ.get("OPENAI_API_KEY"))

prompt = ChatPromptTemplate.from_messages([
    ("system", "You are world class technical documentation writer."),
    ("user", "{input}")
])

output_parser = StrOutputParser()

chain = prompt | llm | output_parser

response = chain.invoke("how can langsmith help with testing?")