title: wxpython sizers expands issue
body: <p>I have a screen which has 6 grids as follows:</p>
  
  <p><a href="https://i.stack.imgur.com/rYrwS.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/rYrwS.png" alt="enter image description here"></a></p>
  
  <p>I'm adding a 7th grid.
  This causes the screen to look like:</p>
  
  <p><a href="https://i.stack.imgur.com/ntJ1w.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/ntJ1w.png" alt="enter image description here"></a></p>
  
  <p>however I want the screen to be:</p>
  
  <p><a href="https://i.stack.imgur.com/ea3iV.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/ea3iV.png" alt="enter image description here"></a></p>
  
  <p>I tried to do it with flexgrid but it's not working.</p>
  
  <p>This is my code:</p>
  
  <pre><code>sizer_2 = wx.BoxSizer(wx.HORIZONTAL)
  sizer_2.AddSpacer(10)
  
  sizer_4 = wx.BoxSizer(wx.VERTICAL)
  sizer_4.Add(self.grid1, 1, wx.EXPAND, 0)
  sizer_4.AddSpacer(20)
  sizer_4.Add(self.grid4, 1, wx.EXPAND, 0)
  sizer_4.AddSpacer(20)
  sizer_4.Add(self.grid7, 1, wx.EXPAND, 0)  
  
  
  sizer_5 = wx.BoxSizer(wx.VERTICAL)
  sizer_5.Add(self.grid2, 1, wx.EXPAND, 0)
  sizer_5.AddSpacer(20)
  sizer_5.Add(self.grid5, 1, wx.EXPAND, 0)
  
  sizer_6 = wx.BoxSizer(wx.VERTICAL)
  sizer_6.Add(self.grid3, 1, wx.EXPAND, 0)
  sizer_6.AddSpacer(20)
  sizer_6.Add(self.grid6, 1, wx.EXPAND, 0)      
  
  
  sizer_3=wx.BoxSizer(wx.HORIZONTAL)
  sizer_3.AddSpacer(20)
  sizer_3.Add(sizer_4, 1, wx.EXPAND, 0)
  sizer_3.AddSpacer(20)
  sizer_3.Add(sizer_5, 1, wx.EXPAND, 0)
  sizer_3.AddSpacer(20)
  sizer_3.Add(sizer_6, 1, wx.EXPAND, 0)
  
  
  sizer_1= wx.BoxSizer(wx.VERTICAL)
  sizer_1.AddSpacer(10)
  sizer_1.Add(sizer_2)
  sizer_1.AddSpacer(20)
  sizer_1.Add(sizer_3, 1, wx.EXPAND, 0)
  
  self.SetSizer(sizer_1)
  self.Layout()
  </code></pre>
  
  <p>What can I do?</p>