[Tutor] Re: Class - superclass

[Andrei]

Bernard Lebel wrote on Fri, 8 Apr 2005 15:05:13 -0400:

> I'm experimenting with basic inheritance concepts, and something that
> I would assume to work returns an error.
> 
>>>> class A:
> ...     def __init__( self ):
> ...             self.a = 13
> ...
>>>> class B( A ): # create sub-class of class A
> ...     def __init__( self ):
> ...             self.b = 14

Call the __init__ of the ancestor explicitly:

>>> class B(A):
...     def __init__(self):
...         A.__init__(self)
...         self.b = 14
>>> b = B()
>>> b.a, b.b
(13, 14)

B inherits everything from A, but by defining B.__init__, the __init__
inherited from A is replaced, so you'll need to call it explicitly. Python
has no way of knowing that you still want to use the original __init__ too
unless you tell it so. To demonstrate the fact that __init__ is indeed
inherited:

>>> class C(A):
...     pass
>>> c = C() # inherited __init__ (A.__init__) is called
>>> c.a
13

-- 
Yours,

Andrei

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