[Tutor] Having trouble with a dictionary of lists

[William Witteman]

I am trying to create a CSV file of sorted similar lists, arranged so
that differences are easily compared in a spreadsheet.  I am
encountering the following error, however:

IndexError: list assignment index out of range

On the indicated line below.  I understand the error, but I don't
understand why I am getting it.  Can anyone shed some light on this?
Thanks.

#!/usr/bin/python

"""
Take a collection of lists, combine them into one list, deleting duplicates.
Sort the list and use it as the leftmost column of a table.  Then put each 
lists contents into the table, one per column, with the elements aligned
with the leftmost (index) column.

"""

import os, sys, csv

def cmpss(filename,*sslists):
  """Write a CSV file from the collection of lists."""

  if os.path.exists(filename):
    print("%s exists: please choose another filename." % filename)
    sys.exit(1)
  else:
    try:
      fn = csv.writer(open(filename, "w"))
    except IOError:
      print("There is a problem opening the requested file.  Sorry.")
      sys.exit(1)

  termdict = {}

  for sslist in sslists:
    for term in sslist:
      termdict[term] = ""
  
  termlist = termdict.keys()
  termlist.sort()

  sortedtermdict = {}
  number_of_commas = 1 - len(sslists)
  
  for term in termlist:
    sortedtermdict[term] = ["" for x in range(number_of_commas)]

  for sslist in sslists:
    counter = 0
    for term in sslist:
# The line below is where my program barfs.
      sortedtermdict[term][counter] = term
    counter = counter + 1

  for row in sortedtermdict:
    fn.writerow(row)
      
-- 

yours,

William