How do I use LangChain with GPT models from OpenAI?

To use LangChain with OpenAI’s GPT models, you start by integrating the LangChain library into your project to streamline interactions with the model. First, install the necessary packages: pip install langchain openai. Next, set up your OpenAI API key, typically stored in an environment variable (e.g., os.environ["OPENAI_API_KEY"] = "your-key"). LangChain provides classes like OpenAI or ChatOpenAI to interface with GPT models. For example, initializing a GPT-3.5-turbo model looks like from langchain.chat_models import ChatOpenAI; llm = ChatOpenAI(model_name="gpt-3.5-turbo"). You then create prompt templates to structure inputs, such as from langchain import PromptTemplate; template = "Write a blog outline about {topic}"; prompt = PromptTemplate(template=template, input_variables=["topic"]). Finally, chain the prompt and model using LLMChain to execute the workflow: from langchain import LLMChain; chain = LLMChain(llm=llm, prompt=prompt); result = chain.run("climate change").

Beyond basic usage, LangChain supports advanced features like memory and agents. Memory allows models to retain context across interactions. For instance, ConversationBufferMemory stores chat history: from langchain.memory import ConversationBufferMemory; memory = ConversationBufferMemory(). You can add this to your chain to enable multi-turn conversations. Agents extend functionality by letting the model decide when to use external tools. For example, a math-solving agent might use a calculator: from langchain.agents import load_tools; tools = load_tools(["llm-math"], llm=llm); agent = initialize_agent(tools, llm, agent="zero-shot-react-description"). The agent can then answer questions like agent.run("What is 15% of 200?") by combining the model’s reasoning with the tool’s calculation.

When using LangChain with GPT models, consider best practices for reliability and efficiency. Handle API errors with retries or fallback logic, as network issues or rate limits (e.g., OpenAI’s tokens-per-minute cap) can disrupt service. Use LangChain’s built-in utilities, like max_retries in the model initialization, to manage retries. Test prompts thoroughly to ensure they guide the model effectively, especially for complex tasks. For cost management, monitor token usage via OpenAI’s API dashboard and adjust parameters like max_tokens in prompts. LangChain simplifies these tasks by abstracting boilerplate code, letting developers focus on application logic. By combining structured prompts, memory, and agents, you can build robust applications—from chatbots to data analysis tools—while maintaining control over model behavior and resource usage.