Unified Type/class

[Alex Martelli]

Pedro Rodriguez wrote:
        ...
>> I'm not sure that it's a problem in Python that the capability is
>> restricted to classes coded in Python. In cases where you need to
        ...
> But I think that you can even restrict this capability on classes by
> providing the apropriate metaclass, something like 'FinalType' with
> a semantic close to 'final' keyword in Java.

Sure -- piece of cake [warning, untested code]:

class finalType(type):
    def __init__(self, name, bases, classdict):
        if bases: raise TypeError, "cannot subclass Final type"
        type.__init__(self, name, bases, classdict)

Just use __metaclass__=finalType in a class body, and that class
won't be subclassable (except by further metaclass tweaks...:-).
As above written, the class itself also won't be able to subclass
any other, but that's easy to remedy too, e.g.:

class finalType2(type):
    def __init__(self, name, bases, classdict):
        if bases and isinstance(bases[0], finalType2):
            raise TypeError, "cannot subclass Final type [2]"
        type.__init__(self, name, bases, classdict)


Alex