def doLayout(self):
    sizer_vert = wx.BoxSizer(wx.VERTICAL)

    sizer_hor_1 = wx.BoxSizer(wx.HORIZONTAL)
    sizer_hor_2 = wx.BoxSizer(wx.HORIZONTAL)

    sizer_vert.Add (sizer_hor_1)
    sizer_vert.Add (sizer_hor_2)		

    btn1 = wx.Button (self, wx.NewId(), "Button 1")
    btn2 = wx.Button (self, wx.NewId(), "Button 2")
    btn3 = wx.Button (self, wx.NewId(), "Button 3")
    btn4 = wx.Button (self, wx.NewId(), "Button 4")

    sizer_hor_1.Add (btn1)
    sizer_hor_1.Add (btn2)

    sizer_hor_2.Add (btn3)
    sizer_hor_2.Add (btn4)

    self.SetSizer(sizer_vert)
    self.Layout()