It’s really easy to build a chat bot with python and google app engine. But a bot without a avatar is difficult to identify.
There’s an XMPP protocol for exchanging user avatars: XEP-0084: User Avatar. http://xmpp.org/extensions/xep-0084.html
But how to implement it? Is it possible to implement the protocol with the xmpp apis supported by GAE?
In short no.
These are the supported protocol extensions.
http://code.google.com/apis/talk/jep_extensions/extensions.html