string slicing

Ishwor ishwor.gurung at gmail.com
Sun Dec 5 22:01:31 CET 2004


I didn't mean to be extremely rude. Just a little bit..~:-). sorry.

On Sun, 05 Dec 2004 12:09:22 -0800, Josiah Carlson <jcarlson at uci.edu> wrote:
> 
[snip]

> 
> Goodness, you got right snippy with the 'intellectual property' thing.
> I'm sorry if it sounded as if I had meant "I came up with this before",
> I did not mean it that way.  What I meant was "good advice", "I've seen
> this advice before", and "I've previously taken note of it".  As an
> aside, I also believe that if Fredrik were concerned about my supposed
> theft of his 'advice IP', he would mention it
> 
> Confusions about 'is' are quite common.  Perhaps every week a new thread
> in regards to object identity is offered, usually asking about integer,
> string or list identity.  I'm not having much luck with the google
> incantation right now, but my email archive is spitting back a thread on
> "interning strings" from early November, which discusses strings and
> identity.
> 
> Really, everyone who is thinking of using 'is' should ask themselves
> whether or not it is truely important to have the same object.  In some
> cases it matters, and in others cases it doesn't matter.  The more
> experience one has with Python and the implementations of algorithms,
> the more obvious such choices will become.
> 
> A perfect example of a case when using 'is' is proper is by Barry Warsaw
> (http://mail.python.org/pipermail/python-dev/2004-March/043224.html):
> 
> missing = object()
> 
> if d.get('somekey', missing) is missing:
>   # it ain't there
> 
> In the case of it not mattering, there was a series of threads in March
> of this year in python-dev, discussing replacing the 'is' operator
> strictly comparing object identity with a 'can be replaced by' operator,
> spelled 'is'.  See the threads entitled "redefining is" here:
> http://mail.python.org/pipermail/python-dev/2004-March/thread.html
> Of course it came out that it didn't happen ('is' is much faster, and
> doesn't require objects to define a mechanism to get at their contents,
> etc.), but it is not uncommon for people who think they want 'is' to
> really want 'can be replaced by', especially in the case of tuples:
> 
> >>> a = tuple(list('hello'))
> >>> b = tuple(list('hello'))
> >>> a == b
> True
> >>> a is b
> False
> >>> CanBeReplacedBy(a, b)
> True
> >>>
> 
> (of course you need a proper implementation of CanBeReplacedBy, of which
> a few are offered in the previously mentioned 'replacing is' threads).
> 
> Now, whether or not knowing what 'is' does, or whether knowing the
> internals in regards to how object identity works, is necessary for
> learning the language, I don't know.  It's been a few years since I was
> a newb, but considering all of the questions regarding 'is' usually
> resulting with python-list saying "you want '=='", I'd offer, 'it is not
> necessary'.
> 
> 
> - Josiah

Thanx. Appreciate it. :)

-- 
cheers,
Ishwor Gurung



More information about the Python-list mailing list