callable virtual method

[Jean-Michel Pichavant]

MRAB wrote:
> Jean-Michel Pichavant wrote:
>> Hi fellows,
>>
>> Does anyone know a way to write virtual methods (in one virtual 
>> class) that will raise an exception only if called without being 
>> overridden ?
>> Currently in the virtual method I'm checking that the class of the 
>> instance calling the method has defined that method as well.
>>
>> Example:
>>
>> class Stream(object):
>>    """Interface of all stream objects"""
>>    def resetStats(self):
>>        """Reset the stream statistics. All values a zeroed except the 
>> date."""
>>        _log.info('Reset statistics of %s' % self)
>>        if self.__class__.resetStats == Stream.resetStats:
>>            raise NotImplementedError()
>>
>> It works but it's tedious, I have to add these 2 lines to every 
>> virtual method, changing the content of the 2 lines.
>>
>> Maybe there is a nice/builtin way to do so (python 2.4)
>>
> Why are you checking which class it's in? The method in the base class
> will be called only if it hasn't been overridden in the subclass.

Sorry guys (means guys *and* gals :op ), I realized I've not been able 
to describe precisely what I want to do.
I'd like the base class to be virtual (aka abstract). However it may be 
abstract but it does not mean it cannot do some usefull stuff.


Here is the schema of my abstract methods :

class Interface(object):
    def method(self):
        # ---------------------
        # some common stuff executed here
        # ---------------------
        print 'hello world'
        # ---------------------
        # here shall stand child specific stuff (empty in the interface 
method)
        # ---------------------
        if self.__class__.method == Interface.method:
            raise NotImplementedError('You should have read the f****** 
manual ! You must override this method.')

class GoodChild(Interface):
    def method(self):
       Interface.method(self) # I want to process the cool stuff done my 
the base Interface
       # ------------------------
       # Specific GoodChild stuff here
       # ------------------------
       print 'I am a good'
       return 'perfect'

class BadChild(Interface):
    pass #I'm too lazy


good = GoodChild()
bad = BadChild()

good.method()
...hello world
...I am a good

bad.method()
...NotImplementedError: You should have read the f****** manual ! You 
must override this method.


The reason I'd like to do so: I'll be providing the Interface, but child 
classes will be overridden by others. Having a reliable error RTFM 
feedback is a time saver, for me and the users.
I hope I clarified my issue.

JM