'Trigger the change of fiscal position when the shipping address is modified.'

@api.multi
@api.onchange('partner_shipping_id', 'partner_id')
def onchange_partner_shipping_id(self):

    self.fiscal_position_id = self.env['account.fiscal.position'].get_fiscal_position(self.partner_id.id, self.partner_shipping_id.id)
    return {}
