Magnus Lycka wrote: > Bryan Olson wrote: > >> Magnus Lycka wrote: >> >>> Bryan Olson wrote: >>> >>>> big_union = set() >>>> for collection in some_iter: >>>> big_union.update(t) >>>> collection.clear() >>> >>> >>> I don't understand the second one. Where did 't' come from? >> >> >> Cut-and-past carelessness. Meant to update with 'collection'. > > > If some_iter gives you dicts, the code above will throw away > your values, and put the set of keys in big_union. Is that what > you meant to do?
It can be quite useful. Python only recently added the set type. Previously, the usual way to implement sets with efficient membership testing was to use a dict where the keys map to some irrelevant value. The above will work for the old technique as well as for the set type. > I suspect most people would find this somewhat > surprising. For sets and "BryanLists" it will put a set of all > the contents of those collections in big_union. That was the description: moving everything from several collections into a single union. > I think this > just verifies my previous arguments. It's rarely meaningful to > write functions that are meaingful for all builtin collections. That's a nonsense argument, polymorphism doesn't have to work over every type to be useful. Functions meaningful for either sets or lists are common; that's enough justification for giving corresponding operations the same interface. -- --Bryan -- http://mail.python.org/mailman/listinfo/python-list
