<!-- content of form view -->

<field name="amount"/>

<field name="unit_price"/>

<field name="price" readonly="1"/>

# onchange handler

@api.onchange('amount', 'unit_price')

def _onchange_price(self):

    # set auto-changing field

    self.price = self.amount * self.unit_price

    # Can optionally return a warning and domains

    return {

        'warning': {

            'title': "Something bad happened",

            'message': "It was very bad indeed",

        }

    }