Alternating Style
Problem: You want to alternate the background color of a list's elements as you dynamically generate it from a passed sequence.
Solution: Give templetor access to the int built-in and use modulo to test.
code.py
web.template.Template.globals['int'] = int
template.html
<ul>
$var i: 0
$for track in tracks:
$var i: ${int(self.i) + 1}
<li class="
$if int(self.i) % 2:
odd
$else:
even
">$track.title</li>
</ul>