Multiple windows

[bgturk]

Hello,

I am using PyQt4 to visualize a fish that changes its shape:

def main():
 
	app = QtGui.QApplication(sys.argv)
 
	scene = QtGui.QGraphicsScene()
	scene.setSceneRect( -2.0, -2.0, 4.0, 4.0)
 
	fish = Fish()
	fish.setPos(0.0, 0.0)
	scene.addItem(fish)
 
	view = QtGui.QGraphicsView(scene)
	view.setRenderHint(QtGui.QPainter.Antialiasing)
	view.scale(150,150)
 
	view.show()
	view.raise_()
 
	sys.exit(app.exec_())

def main():

	app = QtGui.QApplication(sys.argv)
	
	scene = QtGui.QGraphicsScene()
	scene.setSceneRect( -2.0, -2.0, 4.0, 4.0)
		
	fish = Fish()
	fish.setPos(0.0, 0.0)
	scene.addItem(fish)
		
	view = QtGui.QGraphicsView(scene)
	view.setRenderHint(QtGui.QPainter.Antialiasing)
	view.scale(150,150)
	
	view.show()
	view.raise_()
	
	sys.exit(app.exec_())

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So far so good. This code works as expected. It opens up a window, with the fish in it.

Now I would like to simulate several fish, each placed in their own separate main window.

So the first step I did was to define a MainWindow class as follows:

class MainWindow(QtGui.QMainWindow):
 
	def __init__(self):
		QtGui.QMainWindow.__init__(self)
		scene = QtGui.QGraphicsScene()
		scene.setSceneRect( -2.0, -2.0, 4.0, 4.0)
 
		fish = Fish()
		fish.setPos(0, 0)
		scene.addItem(fish)
 
		view = QtGui.QGraphicsView(scene)
		view.setRenderHint(QtGui.QPainter.Antialiasing)
		view.scale(150,150)
		self.setCentralWidget(view)
 
def main():
	app = QtGui.QApplication(sys.argv)
        win = MainWindow()
	win.show()
	win.raise_()
	sys.exit(app.exec_())

class MainWindow(QtGui.QMainWindow):
	
	def __init__(self):
		QtGui.QMainWindow.__init__(self)
		scene = QtGui.QGraphicsScene()
		scene.setSceneRect( -2.0, -2.0, 4.0, 4.0)
			
		fish = Fish()
		fish.setPos(0, 0)
		scene.addItem(fish)
			
		view = QtGui.QGraphicsView(scene)
		view.setRenderHint(QtGui.QPainter.Antialiasing)
		view.scale(150,150)
		self.setCentralWidget(view)

def main():
	app = QtGui.QApplication(sys.argv)
        win = MainWindow()
	win.show()
	win.raise_()
	sys.exit(app.exec_())

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but for some reason this just displays an empty window with no view in it. What am I doing wrong?