---
id: qasync
version: "0.28.0"
license: BSD-2-Clause
license_treatment: permissive
maintenance: active
---

# qasync — Python library for using asyncio in Qt-based applications

License: permissive · Maintenance: active · Downloads: 370.9K/mo

## What it is and what it does

qasync bridges asyncio and Qt by implementing a PEP 3156 event loop that runs inside a Qt application's main thread. This lets you write async/await code directly in PyQt/PySide event handlers and slots, replacing the need for manual threading with cleaner, more readable coroutine-based logic.

The package provides decorators like @asyncSlot and @asyncClose to mark async event handlers, and exposes run_in_executor for CPU-bound work on thread pools. It has no runtime dependencies beyond a Qt binding (PyQt5/6 or PySide2/6) and maintains active development with support for Python 3.8 and later.

Use it for:

- Build responsive Qt GUIs that fetch data from APIs without blocking the UI thread using async/await.
- Replace QThread boilerplate with cleaner asyncio patterns for background tasks in PyQt/PySide apps.
- Coordinate multiple concurrent operations (timers, I/O, network calls) within a single Qt event loop.
- Offload CPU-intensive work to thread pools via run_in_executor while keeping the UI responsive.
- Migrate existing asyncio codebases to Qt-based desktop applications without rewriting async logic.

## Worth the install?

AI-flagged interpretation of the facts above — verify before relying.

qasync integrates asyncio coroutines into PyQt/PySide applications by providing a PEP 3156 event loop, allowing async/await syntax directly in Qt's main thread without threading.

Yes. qasync is actively maintained, has no external dependencies, carries a permissive license, and solves a real pain point—integrating asyncio into Qt apps cleanly. The codebase is stable (Production/Stable classifier), tested across major platforms, and has seen regular updates. Install it if you're building a PyQt/PySide application and want to use async/await instead of threading.

## Install

pip install qasync
uv add qasync
poetry add qasync

## Installing qasync

Before you install: Low friction: pure Python wheel with no runtime dependencies. Actively maintained as of July 2026 with 405 repository stars and a clear maintenance commitment stated in the project.

License in practice: BSD-2-Clause permissive license allows use, modification, and redistribution with minimal restrictions—suitable for both open and closed projects.

Quickstart:

pip install qasync

from qasync import QApplication, QEventLoop
import asyncio

app = QApplication(sys.argv)
loop = QEventLoop(app)
asyncio.set_event_loop(loop)

# Use async functions in Qt slots and event handlers

Requires PyQt5, PyQt6, PySide2, or PySide6 to be installed separately; Python >=3.8 required.

Verify before relying:

- Whether the package works with all four Qt bindings (PyQt5/6, PySide2/6) equally well or has known limitations with any.
- Performance characteristics when running CPU-intensive tasks via QThreadExecutor compared to standard threading approaches.
- Compatibility with recent Python 3.13+ versions given the stated support ceiling of <3.14.

## Package facts

- License: BSD-2-Clause (permissive)
- Python support: supports_current
- Install friction: low
- Maintenance: active
- Downloads: 370.9K/month (top 15,000 on PyPI)
- Known vulnerabilities: none known

## Tags

asyncio in qt applications, pyqt async await, pyside coroutines, qt event loop asyncio, async qt gui, pyqt threading alternative, qt-integration, async-await

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