Question

Have been wondering about this for days now:

I have a basic wxpython program like this:

from MyModule import *

class Form(wx.Panel):
  def __init__(self, parent, id):
    self.gauge = wx.Gauge(...)
    ...
  def ButtonClick(self, event):
    proc = LongProcess()
    while (LongProcess):
      self.gauge.SetValue(LongProcess.status)
      wx.Yield()

which imports the MyModule.py:

from threading import *

class LongProcess(self):
  def __init__(self):
    Thread.__init__(self)
    self.start()
  def run(self):
    for i in range(100):
      Do_something()
      self.status = i  

This updates the gauge according to the value LongProcess.status, as expected. But the while-loop doesn’t seem appropriate as the whole program uses 100% cpu load because it continuously checks the status (not surprising, tho). Is there any way to send the status back to the “mother program” without doing that millions of times per second?

Answer 1

You can instantiate custom events from the non-GUI thread and wx.PostEvent them back to the GUI-thread. This is a thread-safe action. My use cases typically work like this:

• Start worker thread – Custom event ‘Starting Action’
• Start processing
• Post events back updating progress ‘Line 435 of 15000 is parsed’
• etc.

Then I bind the custom event to update a dialog or textctrl/log or whatever. It’s surprisingly easy to do. If you’d like I can post some sample code of a little test case I wrote a while back when I was figuring this stuff out.

–Edit:

Okay here’s some code, first the threading example:

#!usr/bin/env python

import wx
import threading
import Queue
import random
import time

TextEventType = wx.NewEventType()
EVT_THREAD_TEXT_EVENT = wx.PyEventBinder(TextEventType, 1)

global_queue = Queue.Queue()

def threadStart(numthrds, queue, window):
    for i in range(numthrds):
        i = TextThread(queue, window)

class TextThread(threading.Thread):
    def __init__(self, queue, output_window):
        threading.Thread.__init__(self)
        self.inqueue = queue
        self.output_window = output_window
        self.start()


    def run(self):
        word = self.inqueue.get()
        self.setName(word.upper())
        wait = random.randrange(1, 10)
        time.sleep(wait)
        msg = 'Thread: ' + self.getName() + '--wait= ' + str(wait) + ' ' + word
        evt = NewTextEvent(TextEventType, -1)
        evt.setText(msg)
        wx.PostEvent(self.output_window, evt) #post EVT_THREAD_TEXT_EVENT
        #self.inqueue.task_done() #may not need this if non-blocking



class NewTextEvent(wx.PyCommandEvent):
    def __init__(self, evtType, id):
        wx.PyCommandEvent.__init__(self, evtType, id)

        self.msg = ''

    def setText(self, text):
        self.msg = text

    def getText(self):
        return self.msg

class TextFrame(wx.Frame):
    def __init__(self, parent, id, *args, **kwargs):
        wx.Frame.__init__(self, parent, id, *args, **kwargs)
        self.queue = Queue.Queue()
        framesizer = wx.BoxSizer(wx.VERTICAL)
        self.panel = ThreadPanel(self, wx.ID_ANY)
        framesizer.Add(self.panel, 0, wx.EXPAND)
        self.SetSizerAndFit(framesizer)

        self.Bind(EVT_THREAD_TEXT_EVENT, self.OnThreadText)

    def OnThreadText(self, evt):
        msg = evt.getText()
        self.panel.out_tc.AppendText(msg + '\n')

class ThreadPanel(wx.Panel):
    def __init__(self, parent, id, *args, **kwargs):
        wx.Panel.__init__(self, parent, *args, **kwargs)
        vsizer = wx.BoxSizer(wx.VERTICAL)
        self.wordtc = wx.TextCtrl(self, id=wx.ID_ANY, value='', size=(350, -1))
        self.inst_text = wx.StaticText(self, wx.ID_ANY,
            label='Enter a list of space-separated words')
        self.out_tc = wx.TextCtrl(self, id=wx.ID_ANY, size=(350, 300), 
            value='', style=wx.TE_MULTILINE)
        self.start_button = wx.Button(self, wx.ID_ANY, label='Start Threads')

        vsizer.Add(self.inst_text, 0, wx.ALIGN_LEFT)
        vsizer.Add(self.wordtc, 0, wx.EXPAND)
        vsizer.Add(self.start_button)
        vsizer.Add((100,100))
        vsizer.Add(self.out_tc, 0, wx.EXPAND)
        self.SetSizer(vsizer)
        self.Bind(wx.EVT_BUTTON, self.OnStartButton, self.start_button)

    def OnStartButton(self, evt):
        self.out_tc.Clear()
        text = self.wordtc.GetValue()
        self.wordtc.Clear()
        if not text.count(','):
            text = text.split(' ')
        num_thrds = len(text)
        for word in text:
            word = word.strip()
            self.GetParent().queue.put(word)
        threadStart(num_thrds, self.GetParent().queue, self.GetParent())




if __name__ == "__main__":
    app = wx.App()
    frame = TextFrame(None, wx.ID_ANY, 'Thread test')
    frame.Show()    
    app.MainLoop()

And a second, more simple example with custom events:

#!usr/bin/env python

import wx
import random

colorEventType = wx.NewEventType()
EVT_COLOR_EVENT = wx.PyEventBinder(colorEventType, 1)

class ButtonPanel(wx.Panel):
    def __init__(self, parent, *args, **kwargs):
        wx.Panel.__init__(self, parent, *args, **kwargs)

        vsizer = wx.BoxSizer(wx.VERTICAL)
        self.rstbutt = wx.Button(self, wx.ID_ANY, label='Restore')
        self.rstbutt.Disable()
        self.Bind(wx.EVT_BUTTON, self.OnButt, self.rstbutt)
        vsizer.Add(self.rstbutt, 0, wx.ALIGN_CENTER)
        vsizer.Add((500,150), 0)
        self.SetSizer(vsizer)

    def OnButt(self, evt):
        self.SetBackgroundColour(wx.NullColor)
        self.GetParent().Refresh()
        self.rstbutt.Disable()

class ColorEvent(wx.PyCommandEvent):
    def __init__(self, evtType, id):
        wx.PyCommandEvent.__init__(self, evtType, id)
        self.color = None

    def SetMyColor(self, color):
        self.color = color

    def GetMyColor(self):
        return self.color

class MainFrame(wx.Frame):
    def __init__(self, parent, *args, **kwargs):
        wx.Frame.__init__(self, parent, *args, **kwargs)
        framesizer = wx.BoxSizer(wx.VERTICAL)
        self.panel = ButtonPanel(self, wx.ID_ANY)
        framesizer.Add(self.panel, 1, wx.EXPAND)

        menubar = wx.MenuBar()
        filemenu = wx.Menu()
        menuquit = filemenu.Append(wx.ID_ANY, '&Quit')
        menubar.Append(filemenu, 'File')
        colormenu = wx.Menu()
        switch = colormenu.Append(wx.ID_ANY, '&Switch Color')
        menubar.Append(colormenu, '&Color')
        self.SetMenuBar(menubar)

        self.Bind(wx.EVT_MENU, self.OnQuit, menuquit)
        self.Bind(wx.EVT_MENU, self.OnColor, switch)
        self.Bind(EVT_COLOR_EVENT, self.ColorSwitch)
        self.SetSizerAndFit(framesizer)

    def OnQuit(self, evt):
        self.Close()

    def OnColor(self, evt):
        colevt = ColorEvent(colorEventType, -1) 
        colors = ['red', 'green', 'blue', 'white', 'black', 'pink', 
            (106, 90, 205), #slate blue
            (64, 224, 208), #turquoise
            ]
        choice = random.choice(colors)
        colevt.SetMyColor(choice)
        self.GetEventHandler().ProcessEvent(colevt)
        #evt.Skip()

    def ColorSwitch(self, evt):
        color = evt.GetMyColor()
        #print(color)
        self.panel.SetBackgroundColour(color)
        self.Refresh()
        self.panel.rstbutt.Enable()



if __name__ == "__main__":
    app = wx.App()
    frame = MainFrame(None, wx.ID_ANY, title="Change Panel Color Custom Event")
    frame.Show(True)

    app.MainLoop()