def unzip(p, n):
"""Split a list-like object, 'p', into 'n' sub-lists by taking
the next unused element of the main list and adding it to the
next sub-list. A list of tuples (the sub-lists) is returned.
Each of the sub-lists is of the same length; if p%n != 0, the
shorter sub-lists are padded with 'None'.
Example:
>>> unzip(['a','b','c','d','e'], 3)
[('a', 'd'), ('b', 'e'), ('c', None)]
"""
(mlen, lft) = divmod(len(p),n) # find length of longest sub-list
if lft != 0: mlen += 1
lst = [[None]*mlen for i in range(n)] # initialize list of lists
for i in range(len(p)):
(j, k) = divmod(i, n)
lst[k][j] = p[i]
return map(tuple, lst)