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To: python-list@python.org
From: Robert Kern <robert.kern@gmail.com>
Subject: Re: question about numpy, subclassing, and a DeprecationWarning
Date: Wed, 27 Jun 2012 22:57:39 +0100
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On 6/27/12 10:02 PM, Jason Swails wrote:
> Hello,
>
> I'm running into an unexpected issue in a program I'm writing, and I was hoping
> someone could provide some clarification for me.  I'm trying to subclass
> numpy.ndarray (basically create a class to handle a 3D grid).  When I
> instantiate a numpy.ndarray, everything works as expected.  When I call
> numpy.ndarray's constructor directly within my subclass, I get a deprecation
> warning about object.__init__ not taking arguments.  Presumably this means that
> ndarray's __init__ is somehow (for some reason?) calling object's __init__...
>
> This is some sample code:
>
>  >>> import numpy as np
>  >>> class derived(np.ndarray):
> ...     def __init__(self, stuff):
> ...             np.ndarray.__init__(self, stuff)
> ...
>  >>> l = derived((2,3))
> __main__:3: DeprecationWarning: object.__init__() takes no parameters
>  >>> l
> derived([[  8.87744455e+159,   6.42896975e-109,   5.56218818e+180],
>         [  1.79996515e+219,   2.41625066e+198,   5.15855295e+307]])
>  >>>
>
> Am I doing something blatantly stupid?  Is there a better way of going about
> this?  I suppose I could create a normal class and just put the grid points in a
> ndarray as an attribute to the class, but I would rather subclass ndarray
> directly (not sure I have a good reason for it, though).  Suggestions on what I
> should do?

numpy.ndarray does not have its own __init__(), just a __new__(). It's 
__init__() is the same as object.__init__(), which takes no arguments.

[~]
|3> np.ndarray.__init__ is object.__init__
True

There is no need to call np.ndarray.__init__() explicitly.

 
http://docs.scipy.org/doc/numpy/user/basics.subclassing.html#a-brief-python-primer-on-new-and-init

You will also want to ask numpy questions on the numpy mailing list.

   http://www.scipy.org/Mailing_Lists

Personally, I recommend not subclassing ndarray at all. It rarely works out well.

-- 
Robert Kern

"I have come to believe that the whole world is an enigma, a harmless enigma
  that is made terrible by our own mad attempt to interpret it as though it had
  an underlying truth."
   -- Umberto Eco