Question about subclassing and overriding methods

[Frank Millman]

Frank Millman wrote:
> Hi all
>
> Assume a simple class -
>
> class Test(object):
>     def __init__(self,x):
>         self.x = x
>     def getx(self):
>         print self.x
>
> Test(1).getx()
> Test(2).getx()
> Test(3).getx()
>
> As expected, the results are 1,2,3
>
> Assume a slight variation, where given a particular condition I want a
> particular method to behave differently. I know that I could subclass,
> but for various reasons I preferred to do it this way -
>
> class Test(object):
>     def __init__(self,x,y=False):
>         self.x = x
>         if y:
>             self.getx = self.getx2
>     def getx(self):
>         print self.x
>     def getx2(self):
>         print self.x * 2
>
> Test(1).getx()
> Test(2,True).getx()
> Test(3).getx()
>
> As expected, the results are 1,4,3
>
> Now assume a subclass of the above class, where I want the method to
> behave diferently again -
>
> class Test2(Test):
>     def __init__(self,x,y=False):
>         Test.__init__(self,x,y)
>     def getx(self):
>         print self.x*3
>
> Test2(1).getx()
> Test2(2,True).getx()
> Test2(3).getx()
>
> Here I was hoping that the results would be 3,6,9 but they are 3,4,9.
>

Ok, on reflection I more or less understand what is happening, and I
have found an ugly workaround -

class Test2(Test):
   def __init__(self,x,y=False):
        getx = self.getx
        Test.__init__(self,x,y)
        self.getx = getx
    def getx(self):
        print self.x*3

Test2(1).getx()
Test2(2,True).getx()
Test2(3).getx()

Now I get 3,6,9 as intended.

I would still appreciate any comments, especially if someone can
suggest a better approach.

Thanks

Frank