Difference in formatting list and tuple values

[Sue Giller]

I am trying to format values from either a list or a tuple, and I am 
getting the following odd (to me) behavior.   I can format the tuple 
entry using %d, but I get an error when I use the same formatting 
for the same data in a list.
Why does this happen?

>>> l = [1,2,3]						# list
>>> t = (1,2,3)						# tuple
>>> print "%02d" % t[:1]			# format first entry in tuple ok
01
>>> print "%02d" % l[:1]			# get error with list
Traceback (most recent call last):
  File "<interactive input>", line 1, in ?
TypeError: an integer is required
>>> print "%02d" % tuple(t[:1])		# cast to a tuple works ok
01