Good day, i'm making a module that registers social benefits, this is my code:

    def _get_diary_wage(self, cr, uid, ids, field_name, arg, context= None):
        res = {}
        for rec in self.browse(cr,uid,ids,context):
            res[rec.id] = rec.month_wage / 30
        return res
    
    def _get_credit_utilities(self, cr, uid, ids, field_name, arg, context= None):
        res = {}
        for rec in self.browse(cr,uid,ids,context):
            res[rec.id] = (rec.diary_wage * rec.days_utils) / 360
        return res
    
    _columns = {
        'month_wage': fields.float('Month Wage', digits=(16,2)),
        'diary_wage': fields.function(_get_diary_wage, method=True, type='float', string='Diary Wage, store=True),
        'days_utils': fields.integer('Days of Utilities'),
        'credit_utilities': fields.function(_get_credit_utilities, method=True, type='float', string='Credits for Utilities', store=True),
    }
    
    def onchange_month_wage(self, cr, uid, ids, month_wage, context=None):
        vals = {}
        if month_wage > 0:
            vals['diary_wage'] = month_wage / 30
        return {'value': vals}
    
    def onchange_days_utils(self, cr, uid, ids, days_utils, context=None):
        vals = {}
            vals['credit_utilities'] = (diary_wage * days_utils) / 360
        return {'value': vals}

this code calculates the diary_wage perfectly, but when i'm going to calculate the credits_utilities writing the days_utils i get this error:

NameError: global name 'diary_wage' is not defined

Where i'm failing?

I'm working with version 7.

Thanks a lot in advance.