On Tue, Jun 3, 2008 at 9:57 PM, Greg Ewing <greg.ewing@canterbury.ac.nz> wrote:
Brandon Mintern wrote:
Perhaps a better proposal would be "change max to use __iadd__ if available, falling back to __add__ if not"
Obviously, I meant to say "sum" there instead of "max" (which I'm pretty sure you realized as well) -- I had been using max at the time that I wrote that e-mail.
That could change the behaviour of existing code that passes a mutable initial value.
-- Greg
That was my intention, to take advantage of increased efficiency provided by mutable initial values. Unfortunately, I didn't consider the "existing code" problem, but that's not really a problem in Python 3K, is it? For example, sum(lists, []) currently runs in quadratic time (as pointed out by George Sakkis earlier in this thread using an example of sets that implement __add__). If instead, sum was implemented as: def sum (iterable, init=0): for i in iterable: init += i return init Then its behavior would mimic its current behavior for immutable types and other types which do not implement iadd, but for types that allow more efficient value modification, it would be a big win. Is there a good use case for a time when you wouldn't want an initial value to be mutated? In my experience, I've always passed in throwaway initial values anyways, like []. Brandon p.s. Sorry, Greg, for the dupe. Why don't the Python mailing lists generate Reply-To headers? It's pretty annoying to always have to remember to say "Reply to all" instead of simply "Reply".