AI Agent Code Examples 2026 — The Best Working Python Code for Every Concept

All examples use the Anthropic Claude API directly (no framework required). They’re designed to be runnable with minimal setup.

Prerequisites

pip install anthropic
export ANTHROPIC_API_KEY="your-api-key"

Examples

Simple Tool Use

AI Agents: Tools & Tool Use — Basic tool calling with Claude.

Parallel Agents

Multi-Agent Pipelines — Running agents in parallel with asyncio.

MCP Server (Python)

Building MCP Servers — A complete, runnable MCP server in ~50 lines.

ReAct Agent from Scratch

import anthropic
import json

client = anthropic.Anthropic()

TOOLS = [
    {
        "name": "calculator",
        "description": "Evaluate a mathematical expression.",
        "input_schema": {
            "type": "object",
            "properties": {
                "expression": {"type": "string", "description": "Math expression, e.g. '2 + 2'"}
            },
            "required": ["expression"]
        }
    }
]

def calculator(expression: str) -> str:
    try:
        return str(eval(expression, {"__builtins__": {}}))
    except Exception as e:
        return f"Error: {e}"

def run_agent(user_message: str, max_turns: int = 10) -> str:
    messages = [{"role": "user", "content": user_message}]

    for _ in range(max_turns):
        response = client.messages.create(
            model="claude-opus-4-6",
            max_tokens=1024,
            tools=TOOLS,
            messages=messages,
        )

        if response.stop_reason == "end_turn":
            return next(b.text for b in response.content if hasattr(b, "text"))

        # Process tool calls
        messages.append({"role": "assistant", "content": response.content})

        tool_results = []
        for block in response.content:
            if block.type == "tool_use":
                if block.name == "calculator":
                    result = calculator(block.input["expression"])
                    tool_results.append({
                        "type": "tool_result",
                        "tool_use_id": block.id,
                        "content": result,
                    })

        if tool_results:
            messages.append({"role": "user", "content": tool_results})

    return "Max turns reached"

# Run it
result = run_agent("What is 137 * 89 + 42?")
print(result)