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Sub-classing NumArray - two questions

Colin J. Williams cjw at sympatico.ca
Wed Oct 1 12:04:23 EDT 2003 
numarray is a package which is under development and intended to replace 
Numeric, an efficient and operational package. 

One of the classes in numarray is NumArray.  As currently implemented, 
instances of this class are instantiated using factory functions.  This 
appears to restrict the sub-classing of NumArray

Examples: a sub-class Matrix, an array restricted to two dimensions, or 
a sub-class Mix, which combines the NumArray with RecArray (another 
class in the numarray package), or even a sub-class of matrix, Symmetric 
(to use more efficient storage)

These cannot readily be built using factory functions.  This has been 
discussed on the NumPy list 
(http://lists.sourceforge.net/lists/listinfo/numpy-discussion) and the 
question was posed:

    Q1
    Can someone please explain what the "new-classes standard" is?
    (Obviously meeting it is not one of our current goals)

Another related question:

    Q2
    It seems that certain flaws were perceived in Numeric (NumPy),
    developed in 1997 by Jim Hugunin.  Development of numarray was
    started to produce an array package which could become a standard
    Python package.  What were the flaws seen in Numeric?

Colin W.

Background from the NumPY list:

Regarding the "new-classes standard", I can't find much in either the 
Python docs or Alex Martelli's "Python in a Nutshell".  One of the new 
features is a __new__ constructor.

The Python array module doesn't formally have a class and thus it can't 
be sub-classed.  It uses a factory function to create instance objects.

Martelli, in PIAN p74, writes of factory functions being useful when one 
wishes to create instances of different classes depending on some 
condition or for the reuse of an existing instance.

In the Python Cookbook p173, he proposes the use of a factory function 
to get around the limitations of Python 2.1 and earlier.  On page 179, 
he refers to the use of a factory method, again to work around 
limitations before Python 2.2.

My rough and ready definition would include the ability to create an 
instance and initialize
the data in one step.

cjw
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