在 tkinter 的 Tk.after() 方法中使用 async/await 关键字

Question

我正在使用 Python3.5 和 Tkinter 创建一个加密货币交换 API 客户端。我有几个显示器，我想每 10 秒异步更新一次。我可以使用 Tk.after() 每 10 秒更新一次显示，就像本例中的

def updateLoans():
    offers = dd.loanOffers()
    demands = dd.loanDemands()
    w.LoanOfferView.delete(1.0, END)
    w.LoanDemandView.delete(1.0, END)
    w.LoanOfferView.insert(END, offers)
    w.LoanDemandView.insert(END, demands)
    print('loans refreshed')

    root.after(10000, updateLoans)

为了使 after 方法继续每 10 秒连续更新一次，函数 updateLoans() 需要作为可调用函数传递到函数内部的 after() 中。

现在让我难过的部分是，当我使用 python 的新 async 和 await 关键字使此函数异步时

async def updateLoans():
    offers = await dd.loanOffers()
    demands = await dd.loanDemands()
    w.LoanOfferView.delete(1.0, END)
    w.LoanDemandView.delete(1.0, END)
    w.LoanOfferView.insert(END, offers)
    w.LoanDemandView.insert(END, demands)
    print('loans refreshed')

    root.after(10000, updateLoans)

这里的问题是我无法在 after 方法的参数内部等待可调用对象。所以我收到运行时警告。 RuntimeWarning: coroutine 'updateLoans' was never awaited.

我的初始函数调用 IS 放置在事件循环中。

loop = asyncio.get_event_loop()
loop.run_until_complete(updateLoans())
loop.close()

最初显示效果很好，但从不更新。

如何使用 Tk.after 异步持续更新 tkinter 显示？

Answer 1

tk.after 接受普通函数，而不是协程。要运行协程完成，可以使用run_until_complete，就像你第一次做的那样：

loop = asyncio.get_event_loop()
root.after(10000, lambda: loop.run_until_complete(updateLoans()))

此外，不要调用 loop.close()，因为您将再次需要循环。

上述快速修复适用于许多用例。然而，事实是，如果 updateLoans() 由于网络缓慢或远程服务问题而花费很长时间，它将使 GUI 完全无响应。一个好的 GUI 应用程序会希望避免这种情况。

虽然 Tkinter 和 asyncio cannot share an event loop yet, it is perfectly possible to run the asyncio event loop in a separate thread. The main thread then runs the GUI, while a dedicated asyncio thread runs all asyncio coroutines. When the event loop needs to notify the GUI to refresh something, it can use a queue as shown here. On the other hand, if the GUI needs to tell the event loop to do something, it can call call_soon_threadsafe or run_coroutine_threadsafe。

示例代码（未经测试）：

gui_queue = queue.Queue()

async def updateLoans():
    while True:
        offers = await dd.loanOffers()
        demands = await dd.loanDemands()
        print('loans obtained')
        gui_queue.put(lambda: updateLoansGui(offers, demands))
        await asyncio.sleep(10)

def updateLoansGui(offers, demands):
    w.LoanOfferView.delete(1.0, END)
    w.LoanDemandView.delete(1.0, END)
    w.LoanOfferView.insert(END, offers)
    w.LoanDemandView.insert(END, demands)
    print('loans GUI refreshed')

# http://effbot.org/zone/tkinter-threads.htm
def periodicGuiUpdate():
    while True:
        try:
            fn = gui_queue.get_nowait()
        except queue.Empty:
            break
        fn()
    root.after(100, periodicGuiUpdate)

# Run the asyncio event loop in a worker thread.
def start_loop():
    loop = asyncio.new_event_loop()
    asyncio.set_event_loop(loop)
    loop.create_task(updateLoans())
    loop.run_forever()
threading.Thread(target=start_loop).start()

# Run the GUI main loop in the main thread.
periodicGuiUpdate()
root.mainloop()

# To stop the event loop, call loop.call_soon_threadsafe(loop.stop).
# To start a coroutine from the GUI, call asyncio.run_coroutine_threadsafe.

在 tkinter 的 Tk.after() 方法中使用 async/await 关键字

Using async/await keywords with Tk.after() method of tkinter

python

tkinter

python-3.x

python-asyncio

python-3.5