On 01/12/06, Chris Hengge <[EMAIL PROTECTED]> wrote: > Nice! Thank you. > > Curious as to why this happens though... > > >>> list1 = ['1','1','2','3','4'] > >>> list2 = list(set(list1)) > >>> list2 > ['1', '3', '2', '4'] <-- here the order has changed.
For the same reason that dictionaries don't preserve order. Basically, sets are (I think) implemented using a hash table. You can read about hash tables on wikipedia (or many other places), but one of the components of a hash table is a function mapping keys to integers in a particular range. To produce an efficient hash table, you want this function to spread the input out evenly across the range, which means you want random behaviour. Hence you lose the order of strings :-) In fact, you can think of a set as a dictionary where the values are always True (or something), and you only care about the keys. eg: >>> import itertools >>> list1 = ['1', '1', '2', '3', '4'] >>> list2 = dict(zip(list1, itertools.repeat(True))).keys() >>> list2 ['1', '3', '2', '4'] -- John. _______________________________________________ Tutor maillist - Tutor@python.org http://mail.python.org/mailman/listinfo/tutor
