How to create an animation in a QtGui?
===

I'm fairly new to Python and Qt, but I'm trying to create a GUI with some animated graphic elements. I can make a simple animation work; in the following code "class MyView" will work when called but "class GraphicsView" is not animated!
Can anyone help me see the problem?

The problem is in the class GraphicsScene, I think

        import sys
    from PyQt4 import QtGui, QtCore
    
    class MyView(QtGui.QGraphicsView):
        def __init__(self):
            QtGui.QGraphicsView.__init__(self)
    
            self.scene = QtGui.QGraphicsScene(self)
            self.item = QtGui.QGraphicsEllipseItem(-20, -10, 40, 20)
            self.scene.addItem(self.item)
            self.setScene(self.scene)
    
            # Remember to hold the references to QTimeLine and QGraphicsItemAnimation instances.
            # They are not kept anywhere, even if you invoke QTimeLine.start().
            self.tl = QtCore.QTimeLine(1000)
            self.tl.setFrameRange(0, 100)
            self.a = QtGui.QGraphicsItemAnimation()
            self.a.setItem(self.item)
            self.a.setTimeLine(self.tl)
    
            # Each method determining an animation state (e.g. setPosAt, setRotationAt etc.)
            # takes as a first argument a step which is a value between 0 (the beginning of the
            # animation) and 1 (the end of the animation)
            self.a.setPosAt(0, QtCore.QPointF(0, -10))
            self.a.setRotationAt(1, 360)
    
            self.tl.start()
    
    #create the graphicsView which contains the graphicsScene
    class GraphicsView(QtGui.QGraphicsView):
        #initialize and set dragMode and renderHints for everything inside the view
        def __init__(self, parent=None):
            super(GraphicsView, self).__init__(parent)
            
            #the dragMode should be changed to use the rihgt-mousebutton
            self.setDragMode(QtGui.QGraphicsView.ScrollHandDrag)
            
            self.setRenderHint(QtGui.QPainter.Antialiasing)
            self.setRenderHint(QtGui.QPainter.TextAntialiasing)
            
        #crate a zoom function for the mouse-wheel
        def wheelEvent(self, event):
            factor = 1.5 ** (event.delta() / 240.0)
            self.scale(factor, factor)
            
    #create the GraphicsScene containing the main graphics
    class GraphicsScene(QtGui.QGraphicsScene):
            
        def animate(self):
            
            self.animations = range(3)
            
            #move item to position(x,y) at time t
            def animate_to(item,x,y,t):
                
                animation = QtGui.QGraphicsItemAnimation()
                #create a timeline of 1 second
                timeline = QtCore.QTimeLine(2000)
                #number of steps in timeline (100)
                timeline.setFrameRange(0,100)
                #set position at time t
                animation.setPosAt(t, QtCore.QPointF(x,y))
                #apply this to "item"
                animation.setItem(item)
                #add timeline to the animation
                animation.setTimeLine(timeline)
                
                #output of this definition is "animation"
                return animation
                
            self.animations[0] = animate_to(self.geos[0],200,200,0.2)
            self.animations[1] = animate_to(self.geos[1],200,200,0.2)
            self.animations[2] = animate_to(self.geos[2],200,200,0.2)
        
            #animation.timeline().start()
            self.animator.start(2000)
            
            
        def __init__(self, parent=None):
            QtGui.QGraphicsScene.__init__(self, parent)
            #set the size of the scene
            self.setSceneRect(0,0,2000,2000)
            
            #self.addRect(QtCore.QRectF(800,800,200,200))
            
            #---create the scene-geometries ---   
    
            #empty list to hold the geometries
            self.geos = []
            
            #create stuff to add to the scene
            geo_01 = QtGui.QGraphicsEllipseItem(800,800,200,200)
            geo_02 = QtGui.QGraphicsEllipseItem(850,850,300,300)
            geo_03 = QtGui.QGraphicsEllipseItem(900,900,400,400)
            #add stuff to the scene
            self.addItem(geo_01)
            self.addItem(geo_02)
            self.addItem(geo_03)
            
            #put stuff into list so it can be referenced
            self.geos.append(geo_01)
            self.geos.append(geo_02)
            self.geos.append(geo_03)
            
            #----do the animation thing---
            self.animator = QtCore.QTimer()
            
            self.animator.timeout.connect(self.animate)
            
            self.animate()
            
            
    #Create a new class which inherrits from "QtGui.QMainWindow"
    class Example(QtGui.QMainWindow):
        
        def __init__(self):
            #The "super()"-method returns the parrent object of the example-class
            #and it's constructor is called ("__init__")
            super(Example, self).__init__()
            
            self.initUI()
            
        #create the GUI
        def initUI(self):
            
            """---create the buttons---"""
            
            #set a font for the tool-tips
            QtGui.QToolTip.setFont(QtGui.QFont('SansSerif', 10))
                    
            #create a button and a tool-tip for the button
            btn_01 = QtGui.QPushButton('Button', self)
            btn_01.setToolTip('This is a <b>QPushButton</b> widget')
            #resize the button with a recommended size (.sizeHint())
            btn_01.resize(btn_01.sizeHint())
            
            #create a button and a tool-tip for the button
            btn_02 = QtGui.QPushButton('Button', self)
            btn_02.setToolTip('This is a <b>QPushButton</b> widget')
            #resize the button with a recommended size (.sizeHint())
            btn_02.resize(btn_02.sizeHint())
            
            """----create a layout----"""
            
            #create the main widget, which holds the layout
            self.main_widget = QtGui.QWidget(self)
            
            #create a vertical box layout to hold the buttons on the right
            vbox = QtGui.QVBoxLayout()
            vbox.addStretch(1)
            vbox.addWidget(btn_01)
            vbox.addWidget(btn_02)  
            
            #create horizontal box layout to hold the vbox and the main area
            hbox = QtGui.QHBoxLayout()
            
            #store the GraphicsScene in a variable so it is not destroyed
            self.scene = GraphicsScene()
            #add the scene to the GraphicsView
            view = GraphicsView(self.scene)
                    
            hbox.addWidget(view)
            hbox.addStretch(1)
            hbox.addLayout(vbox)
            
            self.main_widget.setLayout(hbox)
            self.setCentralWidget(self.main_widget)
            
            #set the possition and size of the window, then set the window title
            #these methods have been inherited by the "QtGui.QWidget"-class
            self.setGeometry(100, 100, 700, 500)
            self.setWindowTitle("PatternNexus...Maybe?")
            #self.setWindowIcon(QtGui.QIcon('web.png'))
            
            self.show()
        
        def closeEvent(self, event):
            #create a messagebox to confirm quit
            # when QtGui.QWidget is closed the QtGui.QCloseEvent is generated
            # to modify its behaviour the event handler (closeEvent()) must be reinplemented
            
            #create a msgBox with 2 buttons
            #4th argument is the button combination
            #5th argument is the button with initial ketboard focus
            reply = QtGui.QMessageBox.question(self, 'Message',
                "Are you leaving?", QtGui.QMessageBox.Yes | 
                QtGui.QMessageBox.No, QtGui.QMessageBox.No)
    
            #test the return value, is "yes" the event is accepted
            if reply == QtGui.QMessageBox.Yes:
                event.accept()
            else:
                event.ignore()
            
    def main():
        #start the application
        app = QtGui.QApplication(sys.argv)
        ex = Example()
        sys.exit(app.exec_())
    
    #if this module (.py-file) is run as the main program the statement is true
    #if this module is imported the statement will return false
    if __name__ == '__main__':
        main()
        

My main references for coding this is "Rapid GUI programming with python and QT" - chapt. 12, and these links:  http://lateral.netmanagers.com.ar/stories/BBS53.html and http://www.diotavelli.net/PyQtWiki/GraphicsView_-_SimpleAnimation