> This isn't a "cast" in the sense of some less-strongly-typed languages; > it's just a conversion. The `list` function/type iterates over its > argument and turns it into a list. Sets are iterable, so that's all > that's really going on here.
oh :~). Learning experience happening here... Thank you. > The reason that lists don't have set-like methods is because > lists aren't sets -- lists can contain duplicate elements Interesting point -- if that's all there is in it, then lists should have difference and intersection methods. Not because they are the same as sets -- because they are slightly different than sets. In this case it doesn't matter - my lists don't contain duplicate elements this time - but I have worked with lists in money market and in inventory, and finding the intersection and difference for matching off and netting out are standard operations. Still, any built in feature would probably be too simple to use in any but the simplest cases. Steve. "Erik Max Francis" <[EMAIL PROTECTED]> wrote in message news:[EMAIL PROTECTED] > bambam wrote: > >> Excellent. By symmetry, I see that "list" casts the set back into a list. >> >> I wonder why list has not been extended with the same (difference, >> interesection) methods? Casting to set looks a little kludgy: >> >> c = list(set(a)-set(b)) >> I wonder if that is clearer than the explicit loop? > > This isn't a "cast" in the sense of some less-strongly-typed languages; > it's just a conversion. The `list` function/type iterates over its > argument and turns it into a list. Sets are iterable, so that's all > that's really going on here. > > The reason that lists don't have set-like methods is because lists aren't > sets -- lists can contain duplicate elements, whereas sets cannot. You > should use the proper type for your needs; if you want to take two lists, > remove duplicate elements, and then end up with a list, then the > sets-difference-and-then-make-a-list mechanism is appropriate. > > -- > Erik Max Francis && [EMAIL PROTECTED] && http://www.alcyone.com/max/ > San Jose, CA, USA && 37 20 N 121 53 W && AIM, Y!M erikmaxfrancis > It [freedom] must be demanded by the oppressed. > -- Dr. Martin Luther King, Jr. -- http://mail.python.org/mailman/listinfo/python-list
