overriding methods - two questions

[Bruno Desthuilliers]

George Sakkis a écrit :
> On Nov 16, 5:03 pm, Steven D'Aprano <st... at REMOVE-THIS-
> cybersource.com.au> wrote:
> 
>> On Fri, 16 Nov 2007 18:28:59 +0100, Bruno Desthuilliers wrote:
>>>> Question 1:
>>>> Given that the user of the API can choose to override foo() or not, how
>>>> can I control the signature that they use?
>>> While technically possible (using inspect.getargspec), trying to make
>>> your code idiot-proof is a lost fight and a pure waste of time.
>> Worse: it's actually counter-productive!
>>
>> The whole idea of being able to subclass a class means that the user
>> should be able to override foo() *including* the signature. Why do you
>> want to stop them?
> 
> Primarily because of this: http://en.wikipedia.org/wiki/Liskov_substitution_principle.
> 
>> Let me give a practical example:
>>
>> (snip misleading example involving __init__)
> 
> Constructors are in general different from other regular methods
> because you refer explicitly to the class name when creating an
> instance;

Not necessarily. There are (quite a few) cases where you don't know 
which "concrete" class you're instanciating...

> that is, the client writes "f = ContinuedFraction(...)" or
> "f = RegularCF(...)" so it's not necessary to have the same signature
> in __init__. 

import platform
cls = platform.get_the_class()
obj = cls('yadda', 42)