Timothy A. Hochberg
Fri, 29 Aug 1997 17:15:11 -0500 (CDT)
On Fri, 29 Aug 1997, Janko Hauser wrote:
> Hi, I haven't played with it yet, but here is a solution to the
> reshape problem.
> First, reshape does function here, but returns not an UserArray
> >>> a
> UserArray([0, 1, 2, 3, 4, 5, 6, 7, 8])
> >>> reshape(a,(3,3))
> array([[0, 1, 2],
> [3, 4, 5],
> [6, 7, 8]])
> But according to the docs of reshape this is a behavior, which can be
> expected in some sense, because reshape returns a copy.
Yes, but I'd still argue that the natural thing to get back is a copy of
the same type as what you put in. Reshaping a UserArray should really
return a UserArray.
Or maybe not. It doesn't bother me that reshaping a tuple gives me an
array. Hmmmm.... Now I'm thinking you might want both. Numeric.reshape
which has the current behaviour and UserArray.reshape which preserves the
class of the reshaped object.
> reshape is
> also not an builtin function, so I see no way to deal with it in the
> class itself.
The way to deal with this is to shadow the functions from multiarray with
python functions in order to "add extra intelligence to the basic C
functions" (from Numeric.py). In order to fix reshape, for instance, one
could use something like:
def reshape(a, shape):
if type(a) === InstanceType:
return reshape(a, shape)
A bunch of these shadow functions would need to be constructed, but
they're all essentially the same. As I mentioned, UserArray would probably
be a good place for them.
> But the docs emphasize, that one should use
> a.shape=(3,3) for inplace reshaping. This can be handled by the class
> with following method:
> def __setattr__(self,att,value):
> if att == 'shape':
This fix looks good for UserArray. And I could do something similar
for FancyArray. To be honest, I'd completely forgotten that setting shape
reshaped the arrray. I think I would raise an exception when attributes
other than shape get set though.
> >>> c=myUserArray.UserArray(range(9))
> >>> c
> [0 1 2 3 4 5 6 7 8]
> >>> c.shape=(3,3)
> >>> c
> [[0 1 2]
> [3 4 5]
> [6 7 8]]
> If there are some more drawbacks or wishful things for the UserArray
> class, please mention it. I see many useful way to use UserArray, so
> this class should be as powerful as possible.
Well I haven't used UserArray much yet, so my list is pretty short.
* Write shadow functions (I just thought of a clever way to do that.)
* Figure out what __float__ is doing there. As far as I can tell float
never suceeds for UserArrays or Normal arrays, so what is it doing there?
* The indexing on UserArray isn't quite right - sometimes is returns a
copy when it should be returning a reference. This is fixed in FancyArray
Has anyone used UserArray much? Have you had any problems with it?
Successes? I'm mostly just curious...
|Tim Hochberg Research Assistant |
|hochberg <at> wwa.com University of Illinois |
| Electrical Engineering |
MATRIX-SIG - SIG on Matrix Math for Python
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