code: def colex (listoflists,cnums):
      
      global index
      column = 0
      if type(cnums) in [ListType,TupleType]:   # if multiple columns to get
          index = cnums[0]
          column = [x[index] for x in listoflists]
          for col in cnums[1:]:
              index = col
              column = abut(column,[x[index] for x in listoflists])
      elif type(cnums) == StringType:              # if an 'x[3:]' type expr.
          evalstring = 'map(lambda x: x'+cnums+', listoflists)'
          column = eval(evalstring)
      else:                                     # else it's just 1 col to get
          index = cnums
          column = [x[index] for x in listoflists]
      return column
docs: Extracts from listoflists the columns specified in the list 'cnums'
  (cnums can be an integer, a sequence of integers, or a string-expression that
  corresponds to a slice operation on the variable x ... e.g., 'x[3:]' will colex
  columns 3 onward from the listoflists).
  
  Usage:   colex (listoflists,cnums)
  Returns: a list-of-lists corresponding to the columns from listoflists
           specified by cnums, in the order the column numbers appear in cnums