AI Agents & LLMs

# Install: pip install langchain langchain-openai

from langchain_openai import ChatOpenAI
from langchain.agents import AgentExecutor, create_react_agent
from langchain.tools import tool
from langchain_core.prompts import PromptTemplate

# 1. Define a tool the agent can use
@tool
def calculator(expression: str) -> str:
    """Evaluate a math expression. Input: a Python math expression as a string."""
    try:
        return str(eval(expression))
    except Exception as e:
        return f"Error: {e}"

# 2. Define the LLM
llm = ChatOpenAI(model="gpt-4o-mini", temperature=0)

# 3. Create the agent with the ReAct prompt pattern
tools = [calculator]
prompt = PromptTemplate.from_template("""
Answer the question using the tools available.
Tools: {tools}
Tool names: {tool_names}
Question: {input}
Scratchpad: {agent_scratchpad}
""")

agent = create_react_agent(llm, tools, prompt)
executor = AgentExecutor(agent=agent, tools=tools, verbose=True)

# 4. Run the agent
result = executor.invoke({"input": "What is 2 to the power of 10 minus 24?"})
print(result["output"])
# Agent thinks → calls calculator("2**10 - 24") → gets 1000 → returns answer