How to migrate App Engine datastore keys from one application to another

fixkey.py

import os
from google.appengine.ext import db

def fixkey(key):
    """Takes a db.Key (or its string form) and checks to see if it is tied to
    the current application.  If not, the key is recreated for the current
    application and returned as a string.
    """
    app_id = os.environ.get('APPLICATION_ID')
    if isinstance(key, basestring):
        key = db.Key(key)
    if key.app() != app_id:
        newkey = db.Key.from_path(*key.to_path())
    else:
        newkey = key
    return str(newkey)