Multiple Class Inheritance Question

[Alan Gauld]

On Sun, 13 Jul 2003 19:28:15 GMT, YoTuco <not.valid at address.org>
wrote:

> Does (can) an inheritance scheme like this have any adverse effects
> (pitt-falls) for the App class inheriting class 'A' twice? 
> 

> class App(B,C):
>     def __init__(self):
>         B.__init__(self)
>         C.__init__(self)

The way you wrote it no since neither B nor C called A's init
method! But assuming they did then there are obvious potential
problems in calling any method twice. For instance if it modifies
an external global value it will be modified twice... If it
modifies a class value similarly it will be modified twice. But
because those are "obvious" issues the designer can work around
them...

In the case of calling methods implemented by A and inherited by
B or C there is no such problem since the message search
algorithm stops when it finds an implementation so it will only
ever call the method once. Provided you make sure the order 
of B,C in the inheritance list is right fo you then it should be
OK. (Recall that App(B,C) is not the same as App(C,B) )

HTH,

Alan G.
Alan g.
http://www.freenetpages.co.uk/hp/alan.gauld/