Negative array indicies and slice()
ian.g.kelly at gmail.com
Mon Oct 29 18:09:01 CET 2012
On Oct 29, 2012 7:10 AM, "Andrew Robinson" <andrew3 at r3dsolutions.com> wrote:
> I will be porting Python 3.xx to a super low power embedded processor (MSP430), both space and speed are at a premium.
> Running Python on top of Java would be a *SERIOUS* mistake. .NET won't even run on this system. etc.
If that's the case, then running Python at all is probably a mistake.
You know the interpreter alone has an overhead of nearly 6 MB?
> Yes, I realize that.
> But, why can't I just overload the existing __getitem__ for lists and not bother writing an entire class?
You can just overload that one method in a subclass of list. Being
able to monkey-patch __getitem__ for the list class itself would not
be advisable, as it would affect all list slicing anywhere in your
program and possibly lead to some unexpected behaviors.
> Let's try your example exactly as shown...
> "hello world"[aslice]
> Traceback (most recent call last):
> File "<stdin>", line 1, in <module>
> NameError: name 'aslice' is not defined
> WOW. Cool.
> Where did the blanks *actually* get filled in? Or HOW WILL they in your next post?
It appears that Steven omitted the definition of aslice by mistake.
It looks like it should have been:
aslice = slice(4, None, 2)
> Looking at some of the online programming notes -- a slice apparently doesn't use an integer storage variable that is capable of arbitrary expansion. =-O -- and hence, won't work for very large sized lists. That actually explains some crashes I have noted in the past when working with 20 million element lists that I wanted a slice of. I had *plenty* of ram on that system.
20 million is nothing. On a 32-bit system, sys.maxsize == 2 ** 31 -
1. If the error you were seeing was MemoryError, then more likely you
were running into dynamic allocation issues due to fragmentation of
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