[Numpy-discussion] can't resize ndarray subclass

Zachary Pincus zpincus at stanford.edu
Tue Feb 28 13:58:02 EST 2006

Thanks Travis for the replies and the new functionality in the SVN!

I think I have enough (well, maybe once I figure out  
__array_priority__) to get a decent wiki entry for subclassing  
ndarray, and maybe some template subclasses that others can use.

I presume __array_priority__ determines the resulting type when two  
different type arrays are ufunc'd together? The exact mechanism of  
which object gets selected as the parent, etc., is still unclear though.


On Feb 28, 2006, at 1:24 PM, Travis Oliphant wrote:

> Zachary Pincus wrote:
>> However a new problem has me nearly tearing my hair out. Calling  
>> the  resize method on an instance of such a subclass works fine.  
>> However,  calling a method that calls 'self.resize' breaks! And  
>> worse, it  breaks in such a way that then subsequent calls to  
>> resize also break.
> In SVN version of numpy, there is a new keyword argument to resize  
> (refcheck).  If this keyword argument is 0 (it defaults to 1), the  
> reference-count check is not performed.  Thus, if you are sure that  
> your array has not exposed it's memory to another object, then you  
> can set refcheck=0 and the resize will proceed.
> If you really did expose your memory to another object, this could  
> lead to segfaults in exactly the same way that exposing the memory  
> to a Python array (array module) and then later resizing (which  
> Python currently allows) would cause problems.
> Be careful...
> -Travis
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