self.Bind(wx.EVT_SIZE, self.OnSize)
self.Centre()
self.SetSizeWH(400, 300)
self.Show(True)

def OnSize(self, event):
    hsize = event.GetSize()[0] * 0.75
self.SetSizeHints(minW=-1, minH=hsize, maxH=hsize)
self.SetTitle(str(event.GetSize()))
app = wx.App()
SizeEvent(None, 1, 'sizeevent.py')
app.MainLoop()
Изменение размера окна wxPython