PyQt app in seperate thread

[anders]

I am writing a plugin for a piece of software in python, and I want to
start up a PyQt GUI in the plugin, without stalling the main thread
while the gui is running (later i will want to pass messages between
the main thread and the gui thread).

I'm new to pyqt, so I'm probably doing something very silly, but for
the moment I'm just trying to get the first pyqt tutorial example
running in a seperate thread:

----8<--------

import sys
from PyQt4 import QtGui
from PyQt4 import QtCore

class MyThread( QtCore.QThread ):
def __init__( self ):
QtCore.QThread.__init__( self )

def run( self ):
app = QtGui.QApplication( sys.argv )
hello = QtGui.QPushButton( 'Hello world!' )
hello.resize( 500, 500 )
hello.show()
app.exec_()
QtCore.QThread.terminate( )



mt = MyThread()
mt.start()
print 'Main thread continuing...'
mt.wait()
print 'GUI thread finished.'

----8<--------

The app starts up (with a warning WARNING: QApplication was not created
in the main() thread. ). I get a window, but no button, and clicking on
the close button does nothing and I have to force the program to quit.

There's got to be a way to get this working, right? Can anyone help me
along the right path?

Cheers,

Anders

 

[Phil Thompson]

I am writing a plugin for a piece of software in python, and I want to
start up a PyQt GUI in the plugin, without stalling the main thread
while the gui is running (later i will want to pass messages between
the main thread and the gui thread).

I'm new to pyqt, so I'm probably doing something very silly, but for
the moment I'm just trying to get the first pyqt tutorial example
running in a seperate thread:

----8<--------

import sys
from PyQt4 import QtGui
from PyQt4 import QtCore

class MyThread( QtCore.QThread ):
def __init__( self ):
QtCore.QThread.__init__( self )

def run( self ):
app = QtGui.QApplication( sys.argv )
hello = QtGui.QPushButton( 'Hello world!' )
hello.resize( 500, 500 )
hello.show()
app.exec_()
QtCore.QThread.terminate( )



mt = MyThread()
mt.start()
print 'Main thread continuing...'
mt.wait()
print 'GUI thread finished.'

----8<--------

The app starts up (with a warning WARNING: QApplication was not created
in the main() thread. ). I get a window, but no button, and clicking on
the close button does nothing and I have to force the program to quit.

There's got to be a way to get this working, right? Can anyone help me
along the right path?

Read http://doc.trolltech.com/4.2/threads.html

In particular the bit that says that exec_() must be called from the main
thread and not from a QThread.

Phil

 

[anders]

Read http://doc.trolltech.com/4.2/threads.html

In particular the bit that says that exec_() must be called from the main
thread and not from a QThread.

Phil

OK so that's all good... so how do I go about doing what I want then?
Can I set up a window in the second thread and start its event loop
without running the event loop in the core app?

 

[Phil Thompson]

OK so that's all good... so how do I go about doing what I want then?
Can I set up a window in the second thread and start its event loop
without running the event loop in the core app?

No. Read the second sentence of the paragraph I referred to. Also read the
section "QObject Reentrancy".

Phil

 

[anders]

No. Read the second sentence of the paragraph I referred to. Also read the
section "QObject Reentrancy".

Phil

OK I see that now. Thanks for pointing that out. So basically, I can't
do what I want at all. That's a bit of a pain. Is there no way of
tricking Qt into thinking I'm running it in the main thread?

A

 

[Chris Mellon]

OK I see that now. Thanks for pointing that out. So basically, I can't
do what I want at all. That's a bit of a pain. Is there no way of
tricking Qt into thinking I'm running it in the main thread?

It's possible with hackery from C++ but I seriously doubt you can do
it from PyQt.

 

[Diez B. Roggisch]

OK I see that now. Thanks for pointing that out. So basically, I can't

do what I want at all. That's a bit of a pain. Is there no way of
tricking Qt into thinking I'm running it in the main thread?

Maybe you can either invert the thread-roles - that is, run your "main"
application in a thread, and if needed start the Qt-thing, or you might
consider spawning a process and using pyro. Which will work very neat, done
so myself.

Diez

 

[anders]

Maybe you can either invert the thread-roles - that is, run your "main"
application in a thread, and if needed start the Qt-thing, or you might
consider spawning a process and using pyro. Which will work very neat, done
so myself.

Diez

Yeah I was thinking that's going to have to be the way to go... I can't
run the main app in a child thread, so I'll have to spawn the GUI as a
seperate process and communicate with it. Didn't know about pyro
though, thanks for the link. You've used it successfully with PyQt in a
seperate process?

Cheers,

Anders

 

[Diez B. Roggisch]

Yeah I was thinking that's going to have to be the way to go... I can't
run the main app in a child thread, so I'll have to spawn the GUI as a
seperate process and communicate with it. Didn't know about pyro
though, thanks for the link. You've used it successfully with PyQt in a
seperate process?

Yup. I used it to spawn a python interpreter in a subprocess, and
communicate some stuff between that and my main GUI app. The idea was to
have a scriptable application, which allowed you could kill the script.

Diez

 

[Jeremy Sanders]

OK I see that now. Thanks for pointing that out. So basically, I can't
do what I want at all. That's a bit of a pain. Is there no way of
tricking Qt into thinking I'm running it in the main thread?

I have an app which runs Qt in a separate thread and allows the user to send
it python commands from the main thread. Have a look at this code to see
how it works:

http://svn.gna.org/viewcvs/veusz/branches/qt4/embed.py?rev=530&view=markup

Jeremy