>>> import albatross
>>> ctx = albatross.SimpleContext('.')
>>> ctx.locals.names = ['Alex', 'Fred', 'Guido', 'Martin', 'Raymond', 'Tim']
>>> albatross.Template(ctx, '<magic>', '''
... <table>
...  <al-for iter="i" expr="names">
...   <al-tr classexpr="['light', 'dark'][i.index() % 2]" whitespace>
...    <td><al-value expr="i.value()" /></td>
...   </al-tr>
...  </al-for>
... </table>
... ''').to_html(ctx)
>>> ctx.flush_content()
<table>
 <tr class="light">
   <td>Alex</td>
  </tr><tr class="dark">
   <td>Fred</td>
  </tr><tr class="light">
   <td>Guido</td>
  </tr><tr class="dark">
   <td>Martin</td>
  </tr><tr class="light">
   <td>Raymond</td>
  </tr><tr class="dark">
   <td>Tim</td>
  </tr></table>