[Numpy-discussion] Please help with subclassing numpy.ndarray
Stefan van der Walt
stefan@sun.ac...
Tue Feb 6 06:56:01 CST 2007
On Tue, Feb 06, 2007 at 01:06:37PM +0100, Sturla Molden wrote:
>
> > def __new__(cls,...)
> > ...
> > (H, edges) = numpy.histogramdd(..)
> > cls.__defaultedges = edges
> >
> > def __array_finalize__(self, obj):
> > if not hasattr(self, 'edges'):
> > self.edges = self.__defaultedges
>
> IMHO, the preferred way to set an instance attribute is to use __init__
> method, which is the 'Pythonic' way to do it.
I don't pretend to know all the inner workings of subclassing, but I
don't think that would work, given the following output:
In [1]: import numpy as N
In [2]: import numpy as N
In [3]:
In [3]: class MyArray(N.ndarray):
...: def __new__(cls,data):
...: return N.asarray(data).view(cls)
...:
...: def __init__(self,obj):
...: print "This is where __init__ is called"
...:
...: def __array_finalize__(self,obj):
...: print "This is where __array_finalize__ is called"
...:
In [4]: x = MyArray(3)
This is where __array_finalize__ is called
This is where __init__ is called
In [5]: y = N.array([1,2,3])
In [6]: x+y
This is where __array_finalize__ is called
Out[6]: MyArray([4, 5, 6])
Regards
Stéfan
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