#!/usr/bin/env python
     # encoding: utf-8
     #
     # Copyright (c) 2010 Doug Hellmann.  All rights reserved.
     #
     """Demonstrate how insertion order affects dictonaries and sets.
     """
     #end_pymotw_header
     
     def group_by_length(words):
         """Returns a dictionary grouping words into sets by length.
     
         >>> grouped = group_by_length([ 'python', 'module', 'of', 'the', 'week' ])
         >>> grouped == { 2:set(['of']),
         ...              3:set(['the']),
         ...              4:set(['week']),
         ...              6:set(['python', 'module']),
         ...              }
         True
     
         """
         d = {}
         for word in words:
             s = d.setdefault(len(word), set())
             s.add(word)
         return d