Question

In this program I get an error when I use a while True loop in the thread. Without the loop I get no error. Of course in the real program I don’t update a label continuously. Any idea what I’m doing wrong?

This is the program:

import wx
import thread

class Example(wx.Frame):

    def __init__(self, parent): 
        wx.Frame.__init__(self,parent)
        self.InitUI()

    def InitUI(self):
        self.SetSize((250, 200))
        self.Show(True)

        self.text = wx.StaticText(self, label='',pos=(20,30))

        thread.start_new_thread(self.watch,(self,None))

    def watch(self,dummy,e):
        while True:
            self.text.SetLabel('Closed')


def main():
    ex = wx.App()
    Example(None)
    ex.MainLoop()    

if __name__ == '__main__':
    main() 

And this is the error:

Pango:ERROR:/build/pango1.0-LVHqeM/pango1.0-1.30.0/./pango/pango-            layout.c:3801:pango_layout_check_lines: assertion failed: (!layout->log_attrs) Aborted

Any suggestions as to what I’m doing wrong? I’m (obviously) new to threading.

Answer 1

I am not exactly sure if that is what causes you problem, but… You should not interact with the GUI from another thread. You should use wx.CallAfter(). I would consider adding sleep inside the loop also.

wx.CallAfter() documentation says:

Call the specified function after the current and pending event handlers have been completed. This is also good for making GUI method calls from non-GUI threads. Any extra positional or keyword args are passed on to the callable when it is called.

Updated code would than be:

import wx
import thread
import time

class Example(wx.Frame):
    def __init__(self, parent): 
        wx.Frame.__init__(self,parent)
        self.InitUI()

    def InitUI(self):
        self.SetSize((250, 200))
        self.Show(True)

        self.text = wx.StaticText(self, label='',pos=(20,30))

        thread.start_new_thread(self.watch,(self,None))

    def watch(self,dummy,e):
        while True:
            time.sleep(0.1)
            wx.CallAfter(self.text.SetLabel, 'Closed')

def main():
    ex = wx.App()
    Example(None)
    ex.MainLoop()    

if __name__ == '__main__':
    main() 

Maybe you can also consider using wx.Timer.

BTW: Your code runs OK on my PC with Windows 7 and wxPython 2.8.