A few months ago I proposed extending collections to include bags/multisets and setlists (ordered sets/unique lists). If anyone is still interested I have created a PyPI module here: http://pypi.python.org/pypi/data-structures If you want to join the project to file a bug or add something, the project homepage is here: http://code.google.com/p/python-data-structures/ This is the first module I've created so if you could point me to the right list to "promote" it on or point out errors or best practices it would be much appreciated. I know this isn't really the place to be posting about *actual code* but I thought I'd follow up. Thanks, -LenzM