MonkeeSage wrote: > 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. > Keep right on guessing.
> >>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. > OK, so now we appear to be arguing about whether a feature should go into Python because *you* find it to be easier to read and write. But I don't see a groundswell of support from other readers saying "Wow, I've always wanted to do it like that". > >>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 > Nope. In fact d.has_key(k) is a historical spelling, retained only for backwards compatibility, of k in dict. As to the d.get(k, default) method I really don't see a compelling use case despite your protestations, and I don't seem to be alone. Please feel free to start recruiting support. > > 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 > The fact that nobody has listed the good reasons why I shouldn't try to make a computer from mouldy cheese doesn't make this a good idea. regards Steve -- Steve Holden +44 150 684 7255 +1 800 494 3119 Holden Web LLC/Ltd http://www.holdenweb.com Skype: holdenweb http://holdenweb.blogspot.com Recent Ramblings http://del.icio.us/steve.holden -- http://mail.python.org/mailman/listinfo/python-list
