Iteration weirdness

[Dave Opstad]

I'm running into a strange behavior under Python 2.3.3:

------------------------------------------
>>> d = {-1: 'cv', -2: 'se', -3: 'se'}
>>> d
{-1: 'cv', -2: 'se', -3: 'se'}
>>> len(d)
3
>>> [d[-1], d[-2], d[-3]]
['cv', 'se', 'se']
>>> [d[-1-i] for i in len(d)]
Traceback (most recent call last):
  File "<stdin>", line 1, in ?
TypeError: iteration over non-sequence
------------------------------------------

Can someone enlighten me as to why the list comprehension gives an 
error, but the simple list construction case works fine?

Thanks for any help!
Dave Opstad