import wx

class Dialog(wx.Dialog):
    def __init__(self, parent):
        wx.Dialog.__init__(self, parent,
                style = wx.DEFAULT_DIALOG_STYLE | wx.RESIZE_BORDER)
        self.sizer = wx.BoxSizer(wx.VERTICAL)
        self.panel = wx.Panel(self)
        self.panelSizer = wx.BoxSizer(wx.VERTICAL)

        self.button = wx.Button(self.panel, -1, "Show panel")
        self.button.Bind(wx.EVT_BUTTON, self.onbutton)
        self.panelSizer.Add(self.button, wx.ALIGN_CENTER | wx.TOP, 5)
        self.subPanel = wx.Panel(self.panel, -1, size = (600, 400))
        wx.StaticText(self.subPanel, -1, "Some filler text")
        print "Initial size is",self.subPanel.GetSize()
        self.panelSizer.Add(self.subPanel, 1,
                wx.EXPAND | wx.ALIGN_CENTER | wx.ALL, 5)
        self.subPanel.Hide()

        self.panel.SetSizerAndFit(self.panelSizer)
        self.sizer.Add(self.panel)
        self.SetSizerAndFit(self.sizer)


    ## User clicked the show/hide scanning experiment button.
    def onbutton(self, event):
        self.subPanel.Show(not self.subPanel.IsShown())
        self.button.SetLabel("%s panel" % ['Show', 'Hide'][self.subPanel.IsShown()])
        print self.subPanel.GetSize(), self.button.GetSize()
        self.panel.SetSizerAndFit(self.panelSizer)
        print self.panel.GetSize(), self.subPanel.GetSize(), self.button.GetSize()
        self.SetSizerAndFit(self.sizer)

app = wx.App(redirect = False)
frame = wx.Frame(None)
frame.Show()
Dialog(frame).Show()
app.MainLoop()