title: How to pack widgets towards the vertical center of a window in PyGTK?
body: <p>I am using PyGTK to create a GUI:</p>
  
  <pre><code>vbox = gtk.VBox(False, 1)
  vbox.set_border_width(1)
  window.add(vbox)
  vbox.show()
  
  vbox.pack_start(menubar, False, True, 0)
  vbox.pack_start(a, False, False, 0)
  vbox.pack_start(b, False, False, 10)
  vbox.pack_end(self.statusbar, False, False, 0)
  vbox.pack_end(c, False, False, 10)
  </code></pre>
  
  <ul>
  <li><code>a</code> and <code>b</code> are fixed-sized elements.</li>
  </ul>
  
  <p>This creates a window like this:</p>
  
  <pre><code> _______________________
  |_Window____________|_X_|
  |_File_Edit_____________|
  |          [a]          |
  |          [b]          |
  |                       |
  |                       |
  |                       |
  |                       |
  |__________[c]__________|
  |__Status okay._________|
  </code></pre>
  
  <p>I need to center <code>a</code> and <code>b</code> vertically, so that the bottom edge of <code>a</code> appears at vertical center and the top edge of <code>b</code> appears at the vertical center:</p>
  
  <pre><code> _______________________
  |_Window____________|_X_|
  |_File_Edit_____________|
  |                       |
  |           |           |
  |           v           |
  |          [a]          |
  |                       |&lt;-- 10 px margin
  |          [b]          |
  |           ^           |
  |           |           |
  |                       |
  |__________[c]__________|
  |__Status okay._________|
  </code></pre>
  
  <ul>
  <li>Within PyQT4, this layout can be achieved by adding <code>addStretch(1)</code> to the spaces before and after these items, but I cannot find an equivalent command for PyGTK.</li>
  <li>Center can be measured as the space between the file menu and the status bar or the space between the file menu and [c], whichever solution is simplest.</li>
  </ul>
  
  <p>Is there a way to vertically center the items in a window in this way?</p>