Disclaimer: this post has some lousy code and a serious factual error. Throughout, I am speaking about a method of generating all permutations of a set, while saying that I’m speaking about generating all subsets of a set! I have written a newer post which integrates content from a comment by Owen Jacobson, along with a short response explaining just what the heck I was thinking. This post has been left intact aside from this disclaimer for the sake of posterity!

Recently on hackernews, I saw this amazing bunch of vimfu (learned some nifty tricks from it too!), and so I went to check out Jim Dennis’ other answers. Nothing quite so popular, but some worthy reads about “what qualifies a person as a kernel developer” and “can I run a .so compiled in red hat under ubuntu?” – the one that inspired this post though, is the classic “how to generate all subsets of a set?”

Jim suggests using python’s itertools module (in addition to bitmasking on the subset-representation), and I’ve never had cause to look at itertools before. Boy, how I wish I had! I quickly whipped up the following (after reading about argument packing/unpacking:

There’s probably reasons why it’s ugly, and certainly ways to do it better. What I like about this though is that it handles pretty much anything you throw at it, aside from a single non-iterable object I suppose! So calling “all_subsets(1,2,3,4)”, or “all_subsets(‘funny’)”, or “all_subsets([1,2,3,4])” or “all_subsets({‘a’:1,’b’:2})”, or even all_subsets(1) all work and spit out a list of tuples of the permutations.

A possible extension would be to convert back into the form originally provided – but I think that a standard form of return may be more useful. Regardless, this is a neat tool that I will keep in my box.

Edit: I made a modification to the above, so that it can work with any iterable or non-iterable object: