Can't get around "IndexError: list index out of range"

[MonkeeSage]

On Oct 8, 3:05 pm, Steve Holden <s... at holdenweb.com> 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 <fred... at pythonware.com> 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