In odoo-9 first we have to create the three fields in .py file and then add two fields and store it in third fields to click the button to help the get_total function. Then pass get_total function in button.

Use this point show in below:

1- In .py file use this code show in below

 class Feedback(models.Model):
    _name = "feedback"   

    name1 = fields.Integer(string="Subject")
    name2 = fields.Integer(string="Description")
    total = fields.Integer(string="total")
   
    @api.multi
    @api.depends('name1','name2')
    def get_total(self):
        self.total = self.name1 + self.name2
        print"======self.total==========",self.total
    

Feedback()

2- In .xml file use this below code

<?xml version="1.0"?>
<openerp>
<data>

<record id="view_nursery_form77" model="ir.ui.view">
            <field name="name">view.feedback.form</field>
            <field name="model">feedback</field>
            <field name="arch" type="xml">
                <form string="Feedback">
                    <group>
                        <field name="name1" />
                        <field name="name2" />
                        <field name="total" />
                        <button type="object" name="get_total"   string="Calculate Total"/>
                    </group>
                </form>
            </field>
        </record>

<record id="action_nursery33" model="ir.actions.act_window">
            <field name="name">Feedback</field>
            <field name="type">ir.actions.act_window</field>
            <field name="res_model">feedback</field>
            <field name="view_mode">tree,form</field>
        </record>


    <menuitem name="nursery" id="menu_student"/>
    <menuitem name="nursery" id="menu_nursery_item" parent="menu_student" action="action_nursery"/>
   <menuitem name="nursery create" id="menu_nursery_item" parent="menu_student" action="action_nursery33"/>

</data>
</openerp>
  

Output: