qt_await 0.1

Use 'await' syntax with Qt signals

qt-await

This lets you use Python's async & await syntax with PyQt or PySide applications, to wait for Qt signals.

It doesn't integrate Qt with asyncio, trio, or code written for those frameworks.

Usage

To wait for arbitrary signals, wrap them in a SignalQueue. For example, using the QProcess.finished signal:

from PyQt5 import QtCore, QtWidgets
from qt_await import SignalQueue

class MainWindow(QtWidgets.QMainWindow):
    ...

    async def run_subprocess(self):
        proc = QtCore.QProcess()
        sq = SignalQueue(proc.finished)
        proc.start("sleep", ["2"])
        exit_code, exit_status = await sq

There are some helper functions to make common operations easier:

# Pause for 1s (all times are ms, following Qt's convention)
await sleep(1000)

# Pause repeatedly
async for _  in sleep_loop(1000):
    ...

# Wait for something else, with a time limit (also in ms)
await with_timeout(..., 3000)

# Run a QProcess & wait for its finished signal
await run_process(proc, "sleep", ["2"])

# Get streaming bytes from a QIODevice (e.g. a process or a socket)
async for b in read_streaming_bytes(...):
    dest.write(b)

# Similar, but decoding bytes output to strings
async for s in read_streaming_text(...):
    print(s, end='')

All this code needs to be in async def functions, so there are two extra functions to get from normal Qt code into async:

• start_async(f()) starts an async function immediately.
• connect_async(signal, f) connects an async function to a PyQt signal, to start whenever the signal is emitted.

Limitations

This is an experiment, which I mostly wrote for fun - use it at your own risk.

This doesn't integrate with asyncio (see qasync for that) or trio (see qtrio), or any other Python async libraries. It assumes you're doing things the Qt way - QProcess for subprocesses, QThread for threads, QNetworkRequest for HTTP, and so on. It aims to fit in with these APIs as much as possible.

It's also not really an async framework itself. If you want to write significant amounts of async code in Python, trio or asyncio will provide more robust machinery & better abstractions. qt_await just lets you sprinkle a bit of await in your Python Qt code.

Another thing you might want is the qt-async-threads package, which lets you wrap arbitrary slow Python functions in a thread and await their completion, to avoid blocking the event loop.