I hope you got an idea why.
Sourcecode:
<?xml version='1.0' encoding='utf-8'?>
<html xmlns="http://www.w3.org/1999/xhtml" xmlns:py="http://purl.org/kid/ns#">
<head/>
<body>
<table id="map" style="width:500px">
<tr py:for="row in map">
<td py:for="field in row" id="f_${field.x}_${field.y}" class="wall${field.wall} ${field.style}">
</td>
</tr>
</table>
</body>
</html>
Part of the Result:
<tr>
<td id="f_0_(0, 0)" class="wall8 grass"/>
<td id="f_1_(0, 0)" class="wall0 grass"/>
<td id="f_2_(0, 0)" class="wall0 grass"/>
<td id="f_3_(0, 0)" class="wall0 grass"/>
<td id="f_4_(0, 0)" class="wall2 grass"/>
</tr>