hello i want to crreat function that calculate amount_taxed and amount_untaxed

i did this function  but  i cant get tax add to function any solution

class StockPicking(models.Model):
_inherit = 'stock.picking'

amount_untaxed = fields.Float(string='Untaxed Amount', compute='_compute_amounts', store=True)
amount_tax = fields.Float(string='Taxes')
amount_total = fields.Float(string='Total', compute='_compute_amounts', store=True)

@api.depends('move_lines.price_unit', 'move_lines.product_uom_qty')
def _compute_amounts(self):
for picking in self:
amount_untaxed = 0.0
amount_tax = 0.0
amount_total = 0.0
for move in picking.move_lines:

price_unit = move.price_unit
quantity = move.product_uom_qty

amount_total += price_unit * quantity
picking.amount_total = amount_total