In my sales order invoice template I get only one variant attribute of a product.I want to print all variants of a product in my    invoice template.I  tried this below code in report_invoice_document          

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      <t t-set="itr" t-value="0"/>
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           <tr t-foreach="o.invoice_line_ids" t-as="l">
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        <t t-set="itr" t-value="itr+1"/>
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        <td><t t-esc="itr"/></td> 
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           <td><span t-field="l.name"/>
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        ||<span t-field="l.product_id.product_variant_ids"/>   
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        <span t-field="l.product_id.is_product_variant"/>||
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      <span t-field="l.product_id.attribute_line_ids"/>||
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         <span t-field="l.product_id.attribute_value_ids"/></td>

and I get the output                      

[456] pants (Blue, Small)||product.product(2,)True||product.attribute.line(10, 11)||product.attribute.value(1, 4)

Is there any solution to solve this ??