from google.appengine.api import images
from google.appengine.ext import blobstore

def _get_urls_for(self, file_name):
    user = users.get_current_user()
    if user is None:
        return

    bucket_name = app_identity.get_default_gcs_bucket_name()
    path = os.path.join('/', bucket_name, user.user_id(), file_name)
    real_path = '/gs' + path
    key = blobstore.create_gs_key(real_path)
    url = images.get_serving_url(key, size=0)
    thumbnail_url = images.get_serving_url(key, size=150, crop=True)
    return url, thumbnail_url

http://localhost:8080/_ah/img/encoded_gs_file:YXBwX2RlZmF1bHRfYnVja2V0LzE4NTgwNDc2NDIyMDEzOTEyNDExOC9pbWc4NzYuanBn=s32

http://localhost:8080/_ah/img/encoded_gs_file:YXBwX2RlZmF1bHRfYnVja2V0LzE4NTgwNDc2NDIyMDEzOTEyNDExOC9pbWc4NzYuanBn=s150-c