Google Wave Robots: Python Tutorial - Google Wave API - Google Code
Robot Versioning
Robots within the Wave API are versioned. This allows the Wave system to detect when robots have changed and/or their capabilities have been altered. If you modify a robot's capabilities (by adding or removing monitored events, for example), you should also modify the version identifier in the Robot's constructor.
When deploying a robot, the Wave system will check if the robot identifer is different than what it has cached. (The robot identifier is simply a text string.) If so, Wave will refresh the robot and alter the system to generate any new events you've indicated interest in.
app.yaml 的 version 是應用程式的版本，每個版本的檔案會被 GAE 給記起來，所以可以輕易回復到之前的版本。
而 robot 的 version 這個參數則是指定 robot 的 capabilities.xml 是否有變更，若你為這個 robot 新增了一些 event handler，對應的 capabilities.xml 也會更新，就要告訴 GAE 你要重新 cache 新的。
