Py2.3: Feedback on Sets (fwd)
tim.one at comcast.net
Mon Aug 18 06:10:08 CEST 2003
> The real issue with adding a module function or Set method for
> powerset is the lack of compelling use cases; without those, it is
> simply a cute example for the docs or an ASPN recipe.
> Also, if Tim were to chime-in, I think he would abstract the
> problem and say that the algorithm falls in the domain of
> combinatorics (for which he has written a module) and that
> powersets are just a specific case of transforming a collection
> of items into a collection of all possible sub-collections.
It's more that the use cases for generating powersets demand several ways of
+ Lexicographic (if the set elements are totally ordered).
+ Arbitrary Gray code (minimal change from one subset to the next).
+ App-specific Gray code (e.g., from one subset to the next,
add or remove that specific element that makes the largest-- or
smallest --change in the value of a function of the subset).
+ Any order at all (for apps that can't exploit a stronger
guarantee, and want peak generation speed).
one-size-doesn't-fit-anybody-ly y'rs - tim
More information about the Python-list