Re: C++ class inheritance using shadow class

On Thu, 9 Sep 2004, Alexander Tournier wrote:

> I then swig it using shadow classes, that works fine. Now I would like
> to add extra python features to this classes, so I want to use inheritance.
>
>  >>> class Sys(System):
> ...     def __init__(self):
> ...             print Sys.VoxelSize
> ...
>  >>> c = Sys()
> <property object at 0x818ce24>
>  >>> c.VoxelSize
> Traceback (most recent call last):
>   File "<stdin>", line 1, in ?
> TypeError: Type error. Expected _p_System
>  >>>
>
> The inheritance doesn't seem to work! Any reason why that should be??
> Looking forward to your suggestions,

In Python, __init__ does not get called up the inheritance hierarchy like
a C++ constructor.  Your Sys.__init__ does no initialization before trying
to call a member function; no C++ object is instantiated, and the "this"
member is not set (all of that is done by System.__init__).  If you did
not override __init__ in your subclass, the base class __init__ would be
called and all would be well.  If you need to override __init__, putting a
call to System.__init__ at the beginning of Sys.__init__ might get you
what you want.

Josh

--
Joshua L. Cherry, Ph.D.
NCBI/NLM/NIH (Contractor)
jcherry@xxxxxxxxxxxxxxxx


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