adding an attribute to an nd-array

Travis Oliphant oliphant.travis at
Thu Oct 19 09:25:36 CDT 2006

Stefan van der Walt wrote:
> On Wed, Oct 18, 2006 at 09:17:49PM -0400, Pierre GM wrote:
>> On Wednesday 18 October 2006 20:29, Stefan van der Walt wrote:
>>> A quick question on extending numpy arrays: is it possible to easily
>>> add an attribute to an ndarray?
>> It might be easier to create a subclass: pleasehave a look here:
>> That's a tiny example of subclassing ndarrays, with some extra attributes.
>> (BTW, I'm not sure that's the most obvious place where to look: if it turns 
>> out to be useful, I'll put it on the scipy wiki)
> Thanks very much, Pierre.
> If I understand correctly, the following should work:
> import numpy as N
> class InfoArray(N.ndarray):
>     def __new__(info_arr_cls,arr,info={}):
> = info
>         return N.array(arr).view(info_arr_cls)
> When does __array_finalize__ get called, and is it always necessary to
> specify it?
It gets called whenever a new array is created.  No, it is not necessary 
to specify it.


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