停止按钮可在Ipywidgets生态系统中中断while循环

问题描述

让我们假设以下问题：我们有一个Ipywidget按钮和一个进度栏。单击该按钮后，将执行一个函数work（），该函数仅填充进度条直到完成为止，然后反转该过程并将其清空。就目前而言，这种功能是连续运行的。以下代码段提供了相应的MWE：

# importing packages.
from IPython.display import display
import ipywidgets as widgets
import time
import functools

# setting 'progress','start_button' and 'HBox' variables.
progress = widgets.FloatProgress(value=0.0,min=0.0,max=1.0)
start_button = widgets.Button(description="start fill")
HBox = widgets.HBox(children=[start_button,progress])

# defining 'on_button_clicked_start()' function; executes 'work()' function.
def on_button_clicked_start(b,start_button,progress):
    work(progress)

# call to 'on_button_clicked_start()' function when clicking the button.
start_button.on_click(functools.partial(on_button_clicked_start,start_button=start_button,progress=progress))

# defining 'work()' function.
def work(progress):
    total = 100
    i = 0
    # while roop for continuous run.
    while True:
        # while loop for filling the progress bar.
        while progress.value < 1.0:
            time.sleep(0.01)
            i += 1
            progress.value = float(i)/total
        # while loop for emptying the progress bar.
        while progress.value > 0.0:
            time.sleep(0.01)
            i -= 1
            progress.value = float(i)/total
        
# display statement.
display(HBox)

目标是包括“停止”和“恢复”按钮，以便每次单击第一个循环时都会中断while循环，并在按下第二个循环时恢复执行。可以在不使用线程，多处理或异步的情况下做到这一点吗？

解决方法

这是我通过线程包得出的答案，它基于https://ipywidgets.readthedocs.io/en/latest/examples/Widget%20Asynchronous.html中给出的background-working-widget示例。它当然没有经过优化，并且可能不符合良好做法。欢迎提供任何更好答案的人。

# importing packages.
import threading
from IPython.display import display
import ipywidgets as widgets
import time

# defining progress bar 'progress',start,stop and resume buttons
# 'start_button','stop_button' and 'resume_button',and horizontal
# box 'Hbox'.
progress = widgets.FloatProgress(value=0.0,min=0.0,max=1.0)
start_button = widgets.Button(description="start fill")
stop_button = widgets.Button(description="stop fill/empty")
resume_button = widgets.Button(description="resume fill/empty")
Hbox = widgets.HBox(children=[start_button,stop_button,resume_button,progress])

# defining boolean flags 'pause' and 'resume'.
pause = False
restart = False

# defining 'on_button_clicked_start()' function.
def on_button_clicked_start(b):
    # setting global variables.
    global pause
    global thread
    global restart
    # conditinoal for checking whether the thread is alive;
    # if it isn't,then start it.
    if not thread.is_alive():
        thread.start()
    # else,pause and set 'restart' to True for setting
    # progress bar values to 0.
    else:
        pause = True
        restart = True
        time.sleep(0.1)
        restart = False
    # conditional for changing boolean flag 'pause'.
    if pause:
        pause = not pause
    
# defining 'on_button_clicked_stop()' function.    
def on_button_clicked_stop(b):
    # defining global variables.
    global pause
    # conditional for changing boolean flag 'pause'.
    if not pause:
        pause = not pause
        
# defining 'on_button_clicked_resume()' function.
def on_button_clicked_resume(b):
    # defining global variables.
    global pause
    global restart
    # conditional for changing boolean flags 'pause' and 'restart'
    # if necessary.
    if pause:
        if restart:
            restart = False
        pause = not pause

# call to 'on_button_clicked_start()' function when clicking the button.
start_button.on_click(on_button_clicked_start)
# call to 'on_button_clicked_stop()' function when clicking the button.
stop_button.on_click(on_button_clicked_stop)
# call to 'on_button_clicked_resume()' function when clicking the button.
resume_button.on_click(on_button_clicked_resume)

# defining the 'work()' function.
def work(progress):
    # setting global variables.
    global pause
    i = 0
    i_m1 = 0
    # setting 'total' variable.
    total = 100
    # infinite loop.
    while True:
        # stop/resume conditional.
        if not pause:
            # filling the progress bar.
            if (i == 0) or i > i_m1 and not pause:
                time.sleep(0.1)
                if i == i_m1:
                    pass
                else:
                    i_m1 = i
                i += 1
                progress.value = float(i)/total
            # emptying the progress bar.
            if (i == 101) or i < i_m1 and not pause:
                time.sleep(0.1)
                if i == i_m1:
                    pass
                else:
                    i_m1 = i
                i -= 1
                progress.value = float(i)/total
        else:
            if restart:
                i = 0
                i_m1 = 0

# setting the thread.
thread = threading.Thread(target=work,args=(progress,))
# displaying statement.
display(Hbox)