Re: [Numpy-discussion] adding an attribute to an nd-array

[Pierre GM <pgm...@gm...>]

> > >class InfoArray(N.ndarray):
> > >    def __new__(info_arr_cls,arr,info={}):
> > >        info_arr_cls.info = info
> > >        return N.array(arr).view(info_arr_cls)
>
> One has to be careful of this approach.  It ads *the same* information
> to all arrays, i.e.

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'):
            self.info = obj.info
        else:
            self.info = 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.

a = InfoArray(N.array([1,2,3]),{1:1})
b = InfoArray(N.array([1,2,3]),{1:2})

assert a.info=={1:1}
assert b.info=={1:2}
assert (a+1).info==a.info 
assert (b-2).info==b.info