from_date=fields.Date(string="Register date")
final_date=fields.Date(string="Last date")
total_days=fields.Integer(string="TOTAL DAYS")
@api.onchange('total_days','from_date','total_days')
def calculate_date(self):
d1=datetime.strptime(str(self.from_date),'%Y-%m-%d')
d2=datetime.strptime(str(self.final_date),'%Y-%m-%d')
d3=d2-d1
self.total_days=str(d3) . it doesnt work