如何在qweb odoo中打印小计金额

<template id="report_invoice">
    <t t-call="report.html_container">
        <t t-foreach="docs" t-as="doc">
            <div class="page">
                <table class="table table-condensed">
                    <thead>
                        <tr>
                            <th>Product</th>
                            <th>Quantity</th>
                            <th>Price</th>
                        </tr>
                    </thead>
                    <tbody>
                        <t t-set="subtotal" t-value="0"/>
                        <t t-foreach="doc.invoice_line_ids" t-as="line">
                            <tr>
                                <td><t t-esc="line.product_id.name"/></td>
                                <td><t t-esc="line.quantity"/></td>
                                <td><t t-esc="line.price_unit"/></td>
                            </tr>
                            <t t-set="subtotal" t-value="subtotal + line.price_subtotal"/>
                        </t>
                        <tr>
                            <td colspan="2">Subtotal:</td>
                            <td><t t-esc="subtotal"/></td>
                        </tr>
                    </tbody>
                </table>
            </div>
        </t>
    </t>
</template>