On 2009-01-29 15:33, Alan G Isaac wrote:
On Thu, Jan 29, 2009 at 10:01 AM, Alan G Isaac <alan.is...@gmail.com>
wrote:
2. It seems that slice objects and range objects are
awfully similar in many ways. Is this "appearance only",
or was there any discussion of unifying them?
Curious for insight...
On 1/29/2009 1:37 PM Chris Rebert apparently wrote:
Wouldn't really be possible, IMHO. True, they both have notions of
start, stop, and step, but slices don't make sense as ranges without
knowing the length of the container.
Slices seem somewhat more general than ranges.
For example, take the slice
`1:-2:1`. This is somewhat equivalent to range(1, -2, 1). However,
since -2 < 1 (stop < start ) and 1 (the step) is positive, the range
is nonsensical.
Or rather, it makes sense, but is empty.
But I take your point.
However, I would turn it around slightly and ask:
when is it not the case that
range(*slice(start,stop,step).indices(stop)) != range(stop,start,step)
If there are no interesting cases, then it seems
that range might derive from slice.
Just curious...
It's possible that it *could*, but there's also no real benefit to doing so.
You have to replace all the negative indices with calculated positive
indices first in order to have a sensical range(), in this case,
replacing the stop of -2 with len(container)-2.
Also, more fundamentally, Python is liberal in what it allows for the
parts of slices, so unifying slices with ranges would break code. For
example, Python is perfectly happy if I go slice("a",[8],object), none
of which are even numbers.
Ah, this is new in Python 3 I take it?
No.
Python 2.5.1 (r251:54869, Apr 18 2007, 22:08:04)
[GCC 4.0.1 (Apple Computer, Inc. build 5367)] on darwin
Type "help", "copyright", "credits" or "license" for more information.
>>> slice("a",[8],object)
slice('a', [8], <type 'object'>)
I was not aware of this. Use case?
It allows (ab)uses like numpy.mgrid:
>>> mgrid[0:10:11j]
array([ 0., 1., 2., 3., 4., 5., 6., 7., 8., 9., 10.])
--
Robert Kern
"I have come to believe that the whole world is an enigma, a harmless enigma
that is made terrible by our own mad attempt to interpret it as though it had
an underlying truth."
-- Umberto Eco
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