Here is an example with Sale Order Lines which prints the product name of a certain line:

<para style="terp_default_9">[[ [l for l in o.order_line if 'x' in l.name][0].name ]]</para>

... prints the line name of the first line which contains a 'x'. But there will be a problem if no line is selected.

This code prints all lines containing a 'x':

<section>[[repeatIn([l for l in o.order_line if 'x' in l.name],'line')]]
    <para style="terp_default_1">[[ line.name ]]</para>
</section>