wxpython hole in transparent background attempt

hole.pyw

import wx

class Frame(wx.Frame):
    def __init__(self):
        super(Frame, self).__init__(None)

        self.Bind(wx.EVT_KEY_DOWN, self.OnKeyDown)
        self.Bind(wx.EVT_PAINT, self.OnPaint)
        self.SetTransparent(200)

    def OnKeyDown(self, event):
        if event.GetKeyCode() == wx.WXK_ESCAPE:
            self.Close()
        else:
            event.Skip()
    def OnPaint(self, event):
        w, h = self.GetSize()
        dc = wx.PaintDC(self)
        dc.SetBrush(wx.BLUE_BRUSH)
        region = wx.RegionFromPoints([(0, 0), (w, 0), (w, h), (0, h)])
        box = wx.RegionFromPoints([(100, 100), (500, 100), (500, 500), (100, 500)])
        region.SubtractRegion(box)
        dc.SetClippingRegionAsRegion(region)
        dc.DrawRectangle(0, 0, w, h)

if __name__ == '__main__':
    app = wx.PySimpleApp()
    frame = Frame()
    frame.ShowFullScreen(True)
    app.MainLoop()