'''Proof of concept 2: integrate tkinter and async iterator.

Terry Jan Reedy, 2016 July 19
Run with 'python -i' or from IDLE editor to keep tk window alive.

This version uses async for loop and async timer to update tk label.
See tkloop.py for other comments.
'''

import asyncio
import tkinter as tk
import datetime

root = tk.Tk()
loop = asyncio.SelectorEventLoop()
#loop = asyncio.ProactorEventLoop()
#loop = asyncio.get_event_loop()
asyncio.set_event_loop(loop)

class atimer():
    "Yield n or n+1 ticks (None) at intervals."

    def __init__(self, n, interval, tick0=False):
        "Yield initial tick if tick0."
        self.interval = interval
        self.tick0 = tick0
        self.end_time = loop.time() + (n + .9) * interval

    async def __aiter__(self): 
        return self

    async def __anext__(self):
        if self.tick0:
            self.tick0 = False
            return
        await asyncio.sleep(self.interval)
        if loop.time() <= self.end_time:
            return
        else:
            raise StopAsyncIteration

def flipbg(widget, color):
    bg = widget['bg']
    print('click', bg, loop.time())
    widget['bg'] = color if bg == 'white' else 'white'

async def display_date(n, interval):
    hello = tk.Label(root, text='Hello World', bg='white')
    flipper = tk.Button(root, text='Change hello background', bg='yellow',
                        command=lambda: flipbg(hello, 'red'))
    label = tk.Label(root)
    hello.pack()
    flipper.pack()
    label.pack()
    root.update()
    async for tick in atimer(n, interval, tick0=True):
        print(datetime.datetime.now())
        label['text'] = datetime.datetime.now()

def tk_update():
    root.update()
    loop.call_later(.01, tk_update)
tk_update()
loop.run_until_complete(display_date(10, 1.0))
loop.close()