On Tue, Sep 29, 2009 at 13:19, Keith Goodman <kwgoodman@gmail.com> wrote:

I ran across a problem while using numpy. But the problem is more of python problem. I hope I am not too far off topic.

I have a class and a subclass:

class myclass:

   def __init__(self, x):        self.x = x

   def __getitem__(self, index):        if type(index) is slice:            x = self.x[index]            return myclass(x)        else:            raise IndexError, 'Only slicing is allowed in this example.'

   def calc(self):        print 'myclass'

   def __repr__(self):        return self.x.__repr__()

class mysubclass(myclass):

   def calc(self):        print 'mySUBclass'

I can make an instance of mysubclass:

...

...

sub = mysubclass(np.array([1,2,3])) sub   array([1, 2, 3]) sub.calc() mySUBclass

The problem occurs when I slice:

...

...

sub_slice = sub[1:] sub_slice.calc() myclass  # <--- Oops. I'd like this to be mySUBclass

Slicing causes sub to change from mysubclass to myclass. It does so because __getitem__ returns myclass(x). I could make a __setitem__ method in mysubclass that returns mysubclass(x), but I have many such methods with the same problem (not shown in the code above). Is there another solution?

def __getitem__(self, index): if type(index) is slice: x = self.x[index] return type(self)(x) # <---------- else: raise IndexError, 'Only slicing is allowed in this example.' -- 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