Serialize an entity key to a string in Python for GAE
str(entity.key()) will return a base64-encoded representation of the key.
entity.key().name() or entity.key().id() will return just the name or ID, omitting the kind and the ancestry.
In the Java low-level API, there is a way to turn an entity key into a string so you can pass it around to a client via JSON if you want.  Is there a way to do this for python?