check instances of QtWidget in Panel

from PySide import QtGui

class TestWidget(QtGui.QLabel):
    def __init__(self, parent=None):
        self.checkInstances()
        super(TestWidget, self).__init__(parent)

        self.setObjectName('myID')
        self.setText('only show me once')

    def checkInstances(self):
        print 'new instance:', self
        for widget in QtGui.QApplication.allWidgets():
            name = widget.objectName()
            if type(widget) == type(self):
                print "instance already present"
                p = widget.parentWidget()
                while p:
                    if p.parent() and isinstance(p.parent(), QtGui.QStackedWidget):
                        p.parent().removeWidget(p)
                        p = None
                    else:
                        p = p.parentWidget()


nukescripts.registerWidgetAsPanel('TestWidget', 'test widget', 'myID')