PyQt and Maya, with threading = False?

Question

I've been investigating this problem for 3 days now, without any luck. I'm quite new to all this so maybe there is something I'm missing.

The problem applies to: Maya.cmds, PyMel and evaluated MEL using QThread or just Thread

This code is designed to run on the "mayapy" python interpreter which follows Maya. I've created a short example which re-creates the same error in multiple instances.

One button works, the other one doesn't. But they run the same code.

from PyQt4 import Qt

class doStuff( Qt.QThread ):
    taskProgress = Qt.pyqtSignal(int)

    # --------------------------------------------------------- #
    # Here things start to crash...
    def run( self ):

        # This works
        persp = mel.general.PyNode('persp')
        print persp.translateX.get()

        # This dont work
        poiLights = mel.general.ls( exactType="pointLight" ) 
        for light in poiLights:
            print light

        # This dont work
        geo = mel.general.PyNode('pPyramidShape1')
        print mel.modeling.polyEvaluate( geo, face=True )

        # Emit progress
        self.taskProgress.emit( 1 )

        return
    # END
    # --------------------------------------------------------- #

class ui( Qt.QWidget ):
    def __init__(self, parent=None):
        super(ui, self).__init__(parent)

        # Init QThread
        self.thread = doStuff()

        # Create Widgets
        buttonNo = Qt.QPushButton("Start - Dont work")
        buttonYes = Qt.QPushButton("Start - Works")

        # Setup Layout
        layout = Qt.QVBoxLayout()
        layout.addWidget( buttonYes )
        layout.addWidget( buttonNo )
        self.setLayout( layout )
        self.show()

        # --------------------------------
        # PROBLEM AREA: Button signals

        # This one dont work, but starts the thread correctly.
        self.connect( buttonNo, Qt.SIGNAL("clicked()"), self.thread.start )

        # This one works, but dont start the thread correctly.
        self.connect( buttonYes, Qt.SIGNAL("clicked()"), self.thread.run ) 

        # --------------------------------

        self.thread.taskProgress.connect( self.updateProgress )

        return

    # Feedback progress status
    def updateProgress( self, value ):
        print 'Current progress is:', value

        return

if __name__ == '__main__':

    import sys
    app = Qt.QApplication(sys.path)
    program = ui()

    # init maya
    import pymel.core as mel
    filePath = '/Users/ecker/Dropbox/Scripts/RibExporter/mayaScene3ani.ma'
    mel.openFile( filePath, f=True, o=True )

    sys.exit(app.exec_())

This code creates 2 buttons which start executing the same function when pressed. One executes thread.start and thread.run.

thread.start will make the thread work as it should, being able to feed back data to the Qt interface (for a progress bar), but most of the Maya code will start to return all kinds of errors like this:

Traceback (most recent call last):
  File "/Users/ecker/Dropbox/Scripts/RibExporter/error_recreation2.py", line 22, in run
    poiLights = mel.general.ls( exactType="pointLight" ) 
  File "/Applications/Autodesk/maya2012/Maya.app/Contents/Frameworks/Python.framework/Versions/Current/lib/python2.6/site-packages/pymel/core/general.py", line 969, in ls
    res = _util.listForNone(cmds.ls(*args, **kwargs))
  File "/Applications/Autodesk/maya2012/Maya.app/Contents/Frameworks/Python.framework/Versions/Current/lib/python2.6/site-packages/pymel/internal/pmcmds.py", line 134, in wrappedCmd
    res = new_cmd(*new_args, **new_kwargs)
TypeError: Flag 'long' must be passed a boolean argument

It is a boolean argument, and no matter what arguments I try to give it in what format and ways, it will always give errors very similar to this. At the same line res = new_cmd(*new_args, **new_kwargs) needing a boolean.

I need the thread to start, not just run. Unless there is a different way to do the threading, a workaround?

Answer 1

Maya does not work well with threads. The key here is to use maya.utils.executeInMainThreadWithResult.

http://download.autodesk.com/us/maya/2010help/index.html?url=Python_Python_and_threading.htm,topicNumber=d0e182779

I hope this helps.