At 05:07 AM 9/30/2006, Liam Clarke wrote: >Dick Moores wrote: > > At 03:22 AM 9/30/2006, Liam Clarke wrote: > >> Dick Moores wrote:
> >> A Python list sort is destructive, as you can see - it has modified > >> lst. So, to emphasise that it is destructive, it returns None. You'll > >> find this in most destructive methods and functions in Python. > > > > OK, but returning the new list would seem to make more sense. Is the > > reason sort() doesn't, really only that it is better to emphasize that > > it is destructive? > >Hi Dick, > >According to the guy who runs Python, yup. Got to remember the downside >to destructive functions is that everything in Python is a reference. >For example: > > >>> a = [3,2,1] > >>> b = a > >>> b.sort() > >>> print a >[1, 2, 3] > >If you could use > >y = x.sort() > >to get a copy of the sorted list, you'd find that subtle bugs would >appear and frustrate you. In functional languages like Common Lisp or >Scheme, destructive functions are very clearly marked as such, (in >Scheme, they use exclamation marks - (sort! x) to indicate a destructive >version of (sort x).) as a key part of the functional paradigm is >reducing side effects. > >I believe sorting in place has performance advantages too. > >It's covered in the official FAQ: > >http://www.python.org/doc/faq/general/#why-doesn-t-list-sort-return-the-sorted-list Thanks for the further enlightenment, Liam. Dick _______________________________________________ Tutor maillist - Tutor@python.org http://mail.python.org/mailman/listinfo/tutor
