When you are using api.one decorator in Odoo, take into consideration that it always returns a list. That means even if you return from the method single value, it will add it to a list.
For example, If we add a method that adds five additional hours to the work_hours field’s value, the return value from the method will be added to a list as [total].
from openerp import models, fields, api class PartnerContact(models.Model): _name = 'partner.contact' work_hours = fields.Float(string='Work Hours', index=True) @api.one def compute_work_hours(self) total = self.work_hours + 5 return total >> print self.compute_work_hours() >> [10]