cron job在gae python失败了

I have a script in Google Appengine that is started every 20 minutes by cron.yaml. This works locally, on my own machine. When I go (manually) to the url which starts the script online, it also works. However, the script always fails to complete online, on Google's instances, when cron.yaml is in charge of starting it.I have a script in Google Appengine that is sta