i found this code snippet in one example in matplotlib

class App(wx.App):
   
    def OnInit(self):
        'Create the main window and insert the custom frame'
        frame = CanvasFrame()
        frame.Show(True)

        return True

app = App(0)
app.MainLoop()

i just want to ask what does app = App(0) mean, why do we need 0 for an argument