How to get input from website to field.integer() in Python Odoo

I'm using field.Integer() and I think my question is very easy for an Odoo experts

How to get xml from website to field.integer() in Python ?

I tried this code below but when I change the value in the form, the compute result is not changing. I don't understand where is my mistake.

Regards,

model.py:

name = fields.Char()
biography = fields.Html()
nbr1 = fields.Integer()
result = fields.Integer(compute="_compute_total")    
    
@api.onchange('nbr1')
def _compute_total(self):
    for record in self:
        record.result = 2*self.nbr1

template.xml:

<h3 t-field="person.name"/>
<p>Last modified: <i t-field="person.write_date"/></p>
<div t-field="person.biography"/>
<p>
    <label>nbr1</label> : <input type="number" t-attf-href="person.nbr1" name="nbr1"/>
    <a t-attf-href="perso">
    <t t-esc="person.nbr1"/></a>
</p>
<h3 t-field="person.nbr1"/>
<h3 t-field="person.result"/>