Subclassing numarray's arrays

Colin J. Williams cjw at
Sun Aug 15 01:39:49 CEST 2004

Mizrandir wrote:
> I'd like to subclass numarray's array. I'd like to add some methods
> and override others like __init__. I don't know how to do this and
> haven't found help searching the manual or the web, can someone help?
> For example imagine I just want to do something as simple as making a
> subclass "NewClass" with the __init__ method overridden so that the
> behaviour would be:
>>>>a = NewClass(2)
>>>>print a
> [[2 2]
>  [2 2]]
> How could that be done?
> Thanks in advance, miz.

Numarray wasn't designed with subclassing in mind, but there are
workarounds for most problems.

You might try something like:
import numarray.numarraycore as _num
class NewClass(_num.NumArray):
   def __init__(self, n, a):
     ''' n provides the length of each dimension,
         a is the constant value to be plugged.
     arr= _num.array(sequence= n * n * [a], shape= (n, n))

   def __repr__(self):
     " Return printable representation of instance."
     className= self.__class__.__name__
     className= className.zfill(5).replace('0', ' ')
     arr= self.copy()
     arr.__class__= _num.NumArray
     rep= className + _num.NumArray.__repr__(arr)[5:]
     return rep

   def __str__(self):
     " Return a pretty printed string of the instance."
     stri= self.copy()
     stri.__class__= _num.NumArray
     return _num.NumArray.__str__(stri)

if __name__ == '__main__':
   a= NewClass(2, 2)
   print a
   b= NewClass(3, 4)
   print `b`

I hope that this helps.

Colin W.

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