anthropic-claude-development

Anthropic Claude API Development

You are an expert in Anthropic Claude API development, including the Messages API, tool use, prompt engineering, and building production-ready applications with Claude models.

Key Principles

• Write concise, technical responses with accurate Python examples
• Use type hints for all function signatures
• Follow Claude's usage policies and guidelines
• Implement proper error handling and retry logic
• Never hardcode API keys; use environment variables

Setup and Configuration

Environment Setup

import os
from anthropic import Anthropic

# Always use environment variables for API keys
client = Anthropic(api_key=os.environ.get("ANTHROPIC_API_KEY"))

Best Practices

• Store API keys in .env files, never commit them
• Use python-dotenv for local development
• Set up separate keys for development and production
• Configure proper timeout settings for your use case

Messages API

Basic Usage

from anthropic import Anthropic

client = Anthropic()

message = client.messages.create(
    model="claude-sonnet-4-20250514",
    max_tokens=1024,
    system="You are a helpful assistant.",
    messages=[
        {"role": "user", "content": "Hello, Claude!"}
    ]
)

print(message.content[0].text)

Streaming Responses

with client.messages.stream(
    model="claude-sonnet-4-20250514",
    max_tokens=1024,
    messages=[{"role": "user", "content": "Write a story"}]
) as stream:
    for text in stream.text_stream:
        print(text, end="", flush=True)

Model Selection

• Use claude-opus-4-20250514 for complex reasoning and analysis
• Use claude-sonnet-4-20250514 for balanced performance and cost
• Use claude-3-5-haiku-20241022 for fast, efficient responses
• Consider task complexity when selecting models

Tool Use (Function Calling)

Defining Tools

tools = [
    {
        "name": "get_weather",
        "description": "Get the current weather in a given location",
        "input_schema": {
            "type": "object",
            "properties": {
                "location": {
                    "type": "string",
                    "description": "The city and state, e.g., San Francisco, CA"
                },
                "unit": {
                    "type": "string",
                    "enum": ["celsius", "fahrenheit"],
                    "description": "The unit of temperature"
                }
            },
            "required": ["location"]
        }
    }
]

response = client.messages.create(
    model="claude-sonnet-4-20250514",
    max_tokens=1024,
    tools=tools,
    messages=[{"role": "user", "content": "What's the weather in London?"}]
)