On Oct 8, 3:05 pm, Steve Holden <[EMAIL PROTECTED]> wrote: > No: you are proposing to add features to the sequence interface for > which there are few demonstrable use cases.
If I really wanted to find them, how many instances do you think I could find [in the standard lib and community-respected third-party libs] of sequence index checking like "if 2 < len(seq)" and / or try-excepting like "try: seq[2] ..."? Judging by the fact that there isn't any other way to *safely* handle dynamic sequences (esp. sequences which grow based on side-effects which may or may not be present, depending on the execution path through the code); I'd guess the number is alot higher than you seem to think. > Well I certainly didn't find your last one particularly convincing: the > attempt to reference a non-existent sequence member is almost always a > programming error. Unless you are interacting with user input, or other anomalous data source. And in that case you need to do explicit index checking or wrap your code with a try...except; that or you need a convenience function or method that implements a non-terminating exception, and you just check for the exceptional case, like dictionaries have with get(). I find the latter approach to be easier to read and write (see link below), as well as understand. > I would argue exactly the opposite: the reason why they shouldn't be > implemented is because no good reason has been presented why they *should*. Pretend like there are no dict.has_key and dict.get methods. Can you provide a good reason(s) why they should be implemented? Not necessity -- since you can do the same thing more verbosely. Usefulness? -- Probably; but I think the list methods would also be useful (see above). Succinctness [1]? -- The list methods have the same advantage. Anything else? [1] http://mail.python.org/pipermail/python-dev/1999-July/000594.html On Oct 8, 3:11 pm, Fredrik Lundh <[EMAIL PROTECTED]> wrote: > > Huh? I don't want to treat sequences and mappings as the same thing. > > I'm talking about adding two similar convenience methods for sequences > > as already exist for mappings.so what makes you think you're the first one > > who's ever talked about that? I looked yesterday and only found a few posts. A couple involved Marc-Andre Lemburg, and mxTools, where he has a get() function that works for sequences and mappings; that's not what I'm suggesting. However, I found one from 1997 where he mentioned a patch to python 1.5 which added list.get, but I couldn't find the patch or any discussion of why it was (presumably) rejected. The only other post I found that was relevant was one on the dev-python list (mentioned in the July 1-15 summery [1]). And the only thing mentioned there as a reason against it is that "It encourages bad coding. You shouldn't be searching lists and tuples like that unless you know what you're doing." (Whatever that is supposed to mean!). Just point me to the discussion where the good reasons (or any at all) against my suggestion can be found and I'll be glad to read it. I couldn't find it. [1] http://www.python.org/dev/summary/2006-07-01_2006-07-15/#adding-list-get-and-tuple-get Regards, Jordan -- http://mail.python.org/mailman/listinfo/python-list
