adding an attribute to an nd-array

Stefan van der Walt stefan at
Fri Oct 20 03:47:05 CDT 2006

On Thu, Oct 19, 2006 at 09:03:57PM -0400, Pierre GM wrote:
> Indeed. That's basically why you have to edit your __array_finalize__ .
> class InfoArray(N.ndarray):
>     def __new__(info_arr_cls,arr,info={}):
>         info_arr_cls._info = info
>         return N.array(arr).view(info_arr_cls)
>     def __array_finalize__(self, obj):
>         if hasattr(obj,'info'):
>    =
>         else:
>    = self._info
>         return
> OK, so you end up w/ two attributes 'info' and '_info', the latter having the 
> info you want, the latter playing a temporary placeholder. That looks a bit 
> overkill, but that works pretty nice.

Is there any reason why one can't simply do

class InfoArray(N.ndarray):
    def __new__(info_arr_cls,arr,info={}):
        x = N.array(arr).view(info_arr_cls) = info
        return x
    def __array_finalize__(self, obj):
        if hasattr(obj,'info'):


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