How to track state when iterating in Python's Mako Templates

Question

I want to loop over a list and print the elements seperated by ',', with no trailing comma. I can't just ', '.join(headings) because of the formating and escaping. But the following obviously leaves me with a trailing comma.

% for x in headings:
  <a href='#${x|u}'>${x}</a>, \
% endfor

Or more generally: When iterating over something in a Mako template, is there a way to know if I reached the last element (or first, or nt)?

Answer 1

I do stuff like this:

<%def name="format( item )"><a href="#${item|u}">${item|u}</a>
</%def>

${', '.join( format(item) for item in l)}

Answer 2

To keep track of the first or last leg through the loop, in Mako like in plain Python, use:

% for i, x in enumerate(headings): 

so i is 0 on the first leg and len(headings) - 1 on the last leg.

Answer 3

Extending on @AlexMartelli's answer, I like to couple the enumerate thing with a nice trick to keep the instruction small:

% for i, x in enumerate(xs):
  ${','*bool(i)} ${x}
% endfor