---

name: python-async description: Async Python patterns via asyncio and aiohttp for I/O-bound concurrency. Use when adding async APIs, handling concurrent I/O, or debugging async code. globs: "**/*.py" alwaysApply: false category: async tags:

• python
• async
• asyncio
• concurrency
• await
• coroutines tools: [] usage_patterns:
• async-api-development
• concurrent-io
• websocket-servers
• background-tasks complexity: intermediate model_hint: standard estimated_tokens: 400 progressive_loading: true modules:
• modules/basic-patterns.md
• modules/concurrency-control.md
• modules/error-handling-timeouts.md
• modules/advanced-patterns.md
• modules/testing-async.md
• modules/real-world-applications.md
• modules/pitfalls-best-practices.md

---

Async Python Patterns

asyncio and async/await patterns for Python applications.

Quick Start

import asyncio

async def main():
    print("Hello")
    await asyncio.sleep(1)
    print("World")

asyncio.run(main())

When To Use

• Building async web APIs (FastAPI, aiohttp)
• Implementing concurrent I/O operations
• Creating web scrapers with concurrent requests
• Developing real-time applications (WebSockets)
• Processing multiple independent tasks simultaneously
• Building microservices with async communication

When NOT To Use

• CPU-bound optimization - use python-performance instead
• Testing async code - use python-testing async module

Modules

This skill uses progressive loading. Content is organized into focused modules:

• See modules/basic-patterns.md - Core async/await, gather(), and task management
• See modules/concurrency-control.md - Semaphores and locks for rate limiting
• See modules/error-handling-timeouts.md - Error handling, timeouts, and cancellation
• See modules/advanced-patterns.md - Context managers, iterators, producer-consumer
• See modules/testing-async.md - Testing with pytest-asyncio
• See modules/real-world-applications.md - Web scraping and database operations
• See modules/pitfalls-best-practices.md - Common mistakes and best practices

Load specific modules based on your needs, or reference all for detailed guidance.

Exit Criteria

• Async patterns applied correctly
• No blocking operations in async code
• Proper error handling implemented
• Rate limiting configured where needed
• Tests pass with pytest-asyncio

Troubleshooting

Common Issues

RuntimeError: no current event loop Use asyncio.run() as the entry point. Avoid get_event_loop() in Python 3.10+.

Blocking call in async context Move sync I/O to asyncio.to_thread() or loop.run_in_executor().

Tests hang indefinitely Ensure pytest-asyncio is installed and test functions are decorated with @pytest.mark.asyncio.