title: python: how to use win32api.PostMessage
body: <p>I use python to send a key to an application.</p>
  
  <p>I use <code>win32gui</code>:</p>
  
  <p><code>hwndMain = win32gui.FindWindow(None,"busmaster")</code> returns 5441816</p>
  
  <p><code>hwndMain = win32gui.FindWindow(None,"busmaster")</code> returns 3606522</p>
  
  <p>But <code>win32api.PostMessage(hwndChild, win32con.WM_CHAR, ord('a'), 0)</code> returns 0</p>
  
  <p>How can I solve this problem?</p>