import wx

app = wx.PySimpleApp()
frame = wx.Frame(None, title="Nested Sizers")

sizer = wx.BoxSizer(wx.VERTICAL)
sizer1 = wx.BoxSizer(wx.HORIZONTAL)
sizer2 = wx.BoxSizer(wx.HORIZONTAL)

label1 = wx.StaticText(parent=frame, id=-1, label="Upper left")
label2 = wx.StaticText(parent=frame, id=-1, label="Upper right")
label3 = wx.StaticText(parent=frame, id=-1, label="Lower left")
label4 = wx.StaticText(parent=frame, id=-1, label="Lower right")

sizer1.Add(label1, proportion=2, flag=wx.EXPAND | wx.ALL)
sizer1.Add(label2, proportion=1, flag=wx.EXPAND | wx.ALL)
sizer2.Add(label3, proportion=1, flag=wx.EXPAND | wx.ALL)
sizer2.Add(label4, proportion=1, flag=wx.EXPAND | wx.ALL)
sizer.Add(sizer1, proportion=1, flag=wx.EXPAND | wx.ALL)
sizer.Add(sizer2, proportion=3, flag=wx.EXPAND | wx.ALL)

frame.SetSizer(sizer)

frame.Show()
app.MainLoop()