[PyQt] QPainter::end: Painter ended with 2 saved states

[Hans-Peter Jansen]

On Tuesday 28 June 2011, 20:52:12 Eric Frederich wrote:
> I was trying to get an example working with a QThread.
> I wound up creating one but after running it for a while and pressing
> buttons I got the error...
> QPainter::end: Painter ended with 2 saved states
>
> Am I doing something wrong?
> I wanted an example where a worker thread would query a database or
> some other long running operation and leave the GUI responsive
> (although disabling certain elements like the button it was launched
> from).
>
> This is the code I was running....
>
> from PyQt4.QtCore import *
> from PyQt4.QtGui  import *
>
> class Blah(QThread):
>     def __init__(self, parent=None):
>         super(Blah, self).__init__(parent)
>         print 'new thread created'
>
>     def run(self):
>         print 'running'
>         self.parent().setEnabled(False)
>         import time
>         for i in xrange(10):
>             self.parent().setText("%02d" % i)
>             time.sleep(.1)
>         self.parent().setText("Push Me")
>         self.parent().setEnabled(True)

You're doing "bad" things here, that you shouldn't do from a thread, 
e.g. using methods, that trigger redraws. You should create signals in 
your thread, that signals operations to the main thread, where you 
would actually process these operations without fear.

Pete