Piet van Oostrum wrote: >>>>>> Hendrik van Rooyen <hend...@microcorp.co.za> (HvR) wrote: > >> HvR> On Monday 20 July 2009 21:26:07 Phillip B Oldham wrote: >>>> On Jul 20, 6:08 pm, Duncan Booth <duncan.bo...@invalid.invalid> wrote: >>>>> The main reason why you need both lists and tuples is that because a >>>>> tuple of immutable objects is itself immutable you can use it as a >>>>> dictionary key. >>>> Really? That sounds interesting, although I can't think of any real- >>>> world cases where you'd use something like that. > >> HvR> simplest is something like a point in the cartesian plane with >> HvR> an associated attribute like colour. > > There are numerous other examples. Anytime you need a key that is not a > single object but composed of more than one: > Name + birthday > Street + number + City > Student + Course > etc.
Compound keys (like what's listed above) can also be used for sorting lists of dictionaries using DSU style sorting. Something I believe (and I could be wrong) won't work with mutable types like lists. --David -- http://mail.python.org/mailman/listinfo/python-list
