title: How to implement "autoincrement" on Google AppEngine
body: <p>I have to label something in a "strong monotone increasing" fashion. Be it Invoice Numbers, shipping label numbers or the like.</p>
  
  <ol>
  <li>A number MUST NOT BE used twice</li>
  <li>Every number SHOULD BE used when exactly all smaller numbers have been used (no holes).</li>
  </ol>
  
  <p>Fancy way of saying: I need to count 1,2,3,4 ...
  The number Space I have available are typically 100.000 numbers and I need perhaps 1000 a day.</p>
  
  <p>I know this is a hard Problem in distributed systems and often we are much better of with GUIDs. But in this case for legal reasons I need "traditional numbering".</p>
  
  <p>Can this be implemented on Google AppEngine (preferably in Python)?</p>