zero-copy array slicing

[Alex Martelli]

Trevor wrote:

> Is a zero-copy array slicing operation possible?  Or would having two
> arrays share the same elements cause too many problems?  I'm thinking

Perhaps both; in any case, that's what the justly popular Numeric
package does:


> something like:
> 
>>>> a1 = array('b', [0, 1, 2, 3, 4, 5])
>>>> a2 = a1.subsequence(slice(1, 4))
>>>> a2
> array('b', [1, 2, 3])
>>>> a2[0] = 100
>>>> a1
> array('b', [0, 100, 2, 3, 4, 5])

>>> import Numeric
>>> a1=Numeric.arange(5)
>>> a1
array([0, 1, 2, 3, 4])
>>> a2 = a1[1:4]
>>> a2
array([1, 2, 3])
>>> a2[0] = 100
>>> a1
array([  0, 100,   2,   3,   4])
>>>


So if this the behavior you need, the simplest way to get it is exactly 
with the Numeric extensions -- builtin sequences such as lists and 
array.array instances support the safer-but-perhaps-slower approach
of making each slice a copy, differently from what happens when you
slice a Numeric.array.


Alex