Subtract one date from another and get int
Take the difference between two dates, which is a timedelta, and ask for the days attribute of that timedelta.
How can I subtract on datefield from another and get result in integer?
Like 11.05.2015-10.05.2015 will return 1
I tried 
entry.start_devation= each.start_on_fact - timedelta(days=data.calendar_start)