使用 Button Jupyter Notebook 终止循环？

Question

我想：

从串口读取（无限循环）
按下“停止”按钮时 --> 停止读取并绘制数据

来自 How to kill a while loop with a keystroke? 我已经使用键盘中断作为中断示例，这有效，但我想使用按钮。

键盘中断示例

weights = []
times = [] 
#open port 
ser = serial.Serial('COM3', 9600)
try:
   while True: # read infinite loop
       #DO STUFF
       line = ser.readline()   # read a byte string
       if line:
           weight_ = float(line.decode())  # convert the byte string to a unicode string
           time_ = time.time()
           weights.append(weight_)
           times.append(time_)
           print (weight_)
#STOP it by keyboard interup and continue with program 
except KeyboardInterrupt:
   pass
#Continue with plotting

但是我想用一个显示的按钮来做（更容易让人们使用）。我尝试制作一个按钮（in Jupiter Notebook），当按下时 break_cicle=False，但是 当按下按钮时循环不会中断:

 #make a button for stopping the while loop 
button = widgets.Button(description="STOP!") #STOP WHEN THIS BUTTON IS PRESSED
output = widgets.Output()
display(button, output)
break_cicle=True


def on_button_clicked(b):
    with output:
        break_cicle = False # Change break_cicle to False
        print(break_cicle)
        
ser.close()   
button.on_click(on_button_clicked)
ser = serial.Serial('COM3', 9600)
try:
    while break_cicle:

        print (break_cicle)
        line = ser.readline()   # read a byte string
        if line:
            weight_ = float(line.decode())  # convert the byte string to a unicode string
            time_ = time.time()
            weights.append(weight_)
            times.append(time_)
            print (weight_)
except :
    pass

ser.close()

全局不工作的示例

from IPython.display import display
import ipywidgets as widgets

button = widgets.Button(description="STOP!") #STOP WHEN THIS BUTTON IS PRESSED
output = widgets.Output()
display(button, output)
break_cicle=True

def on_button_clicked():
    global break_cicle #added global
    with output:
        
        break_cicle = False # Change break_cicle to False
        print ("Button pressed inside break_cicle", break_cicle)
    
    
button.on_click(on_button_clicked)
try:
    while break_cicle:
        print ("While loop break_cicle:", break_cicle)
        time.sleep(1)
except :
    pass
print ("done")

尽管我按了几次按钮，从下图中你可以看到它从不打印“Button pressed inside break_cicle”。

Answer 1

我认为问题就像在所有 Python 脚本中一样 long-running 代码 - 它运行是一个线程中的所有代码，当它运行是 while True 循环（long-running 代码）然后它不能同时运行其他函数。

您可能必须运行在单独的线程中执行您的函数 - 然后主线程可以执行 on_button_clicked

这个版本适合我：

from IPython.display import display
import ipywidgets as widgets
import time
import threading

button = widgets.Button(description="STOP!") 
output = widgets.Output()

display(button, output)

break_cicle = True

def on_button_clicked(event):
    global break_cicle
    
    break_cicle = False

    print("Button pressed: break_cicle:", break_cicle)
    
button.on_click(on_button_clicked)

def function():
    while break_cicle:
        print("While loop: break_cicle:", break_cicle)
        time.sleep(1)
    print("Done")
    
threading.Thread(target=function).start()

也许 Jupyter 有一些其他方法来解决这个问题 - 即。当你用 async 编写函数时，你可以使用 asyncio.sleep()，当这个函数休眠时，它可以让 Python 到运行其他函数。

编辑：

在互联网上挖掘（使用 Google）我在 Jyputer 论坛上找到 post

Interactive widgets while executing long-running cell - JupyterLab - Jupyter Community Forum

模块 jupyter-ui-poll 有 link，它显示了类似的示例（while-loop + Button），它为此使用 events。当执行函数 pull() 时（在每个循环中），Jupyter 可以将事件发送到小部件并且它有时间执行 on_click().

import time
from ipywidgets import Button
from jupyter_ui_poll import ui_events

# Set up simple GUI, button with on_click callback
# that sets ui_done=True and changes button text
ui_done = False
def on_click(btn):
    global ui_done
    ui_done = True
    btn.description = ''

btn = Button(description='Click Me')
btn.on_click(on_click)
display(btn)

# Wait for user to press the button
with ui_events() as poll:
    while ui_done is False:
        poll(10)          # React to UI events (upto 10 at a time)
        print('.', end='')
        time.sleep(0.1)
print('done')

在 source code 中，我可以看到它为此使用了 asyncio。

编辑：

版本 multiprocessing

进程不共享变量，因此需要 Queue 将信息从一个进程发送到另一个进程。

示例将消息从 button 发送到 function。如果您想将消息从 function 发送到 button，那么最好使用第二个队列。

from IPython.display import display
import ipywidgets as widgets
import time
import multiprocessing

button = widgets.Button(description="STOP!") 
output = widgets.Output()

display(button, output)

queue = multiprocessing.Queue()

def on_button_clicked(event):
    queue.put('stop')
    print("Button pressed")
    
button.on_click(on_button_clicked)

def function(queue):
    
    while True:
        print("While loop")
        time.sleep(1)
        
        if not queue.empty():
            msg = queue.get()
            if msg == 'stop':
                break
            #if msg == 'other text':             
            #    ...other code...
            
    print("Done")
    
multiprocessing.Process(target=function, args=(queue,)).start()

或与上一个更相似

def function(queue):

    break_cicle = True
    
    while break_cicle:
        print("While loop: break_cicle:", break_cicle)
        time.sleep(1)
        
        if (not queue.empty()) and (queue.get() == 'stop'):
            break_cicle = False
        
    print("Done")

编辑：

版本 asyncio

Jupyter 已经运行ning asynio event loop 并且我将 async function 添加到此循环中。并且函数使用 await 函数，例如 asyncio.sleep 所以 asynio event loop 有时间运行其他函数 - 但如果函数可以运行只有标准（不是异步）函数那么它不行。

from IPython.display import display
import ipywidgets as widgets
import asyncio

button = widgets.Button(description="STOP!") 
output = widgets.Output()

display(button, output)

break_cicle = True

def on_button_clicked(event):
    global break_cicle
    
    break_cicle = False

    print("Button pressed: break_cicle:", break_cicle)
    
button.on_click(on_button_clicked)

async def function():   # it has to be `async`
    while break_cicle:
        print("While loop: break_cicle:", break_cicle)
        await asyncio.sleep(1)   # it needs some `await` functions
    print("Done")
    
loop = asyncio.get_event_loop()    
t = loop.create_task(function())  # assign to variable if you don't want to see `<Task ...>` in output

使用 Button Jupyter Notebook 终止循环？

Kill a loop with Button Jupyter Notebook?

python

events

button

break