Loading data into the development server: If you'd like to test how your data works with the app before uploading it, you can load it into the development server. Use the --url option to point the tool at the development server URL.
see more: https://developers.google.com/appengine/docs/python/tools/uploadingdata
appcfg.py upload_data --config_file=album_loader.py --filename=album_data.csv --kind=Album --url=http://localhost:8080/_ah/remote_api <app-directory>