Usefulness of subclassing builtin number types

[Michele Simionato]

Antonio Cuni <TOGLIMIcuni at programmazione.it> wrote in message news:<miqlta.vh4.ln at anto.cuni.lan>...
> Gerhard Häring wrote:
> 
> > I want 'x' to stay of the class MyInt. I even can't think of any use
> > case right now where I'd *not* want this. The problem? Python doesn't
> > do this, instead it always returns ints.
> 
> what about the following?
> 
> def make_wrapper(method_name):
>     def wrapper(self, other):
>         return MyInt(getattr(int, method_name)(self, other))
>     return wrapper
> 
> class MetaInt(type):
>     methods = ['__add__', '__sub__']
>     def __new__(cls, bases, name, dic):
>         for method in MetaInt.methods:
>             dic[method] = make_wrapper(method)
>         return super(MetaInt, cls).__new__(cls, bases, name, dic)
> 
> class MyInt(int):
>     __metaclass__ = MetaInt
> 
> if __name__=='__main__':
>     x = MyInt(3)
>     y = x + 4
>     print y, type(y)
> 
> It seems to work, but I didn't test it very much: obviously it can be 
> improved, e.g. by giving 'int' and 'MyInt' as parameters instead of 
> hard-coded classes.
> 
> ciao Anto

Nice to see other Italians here ! Especially now that there a Big Absent ;-)

BTW, you probably mean  __new__(cls,name,bases,dic) instead of 
__new__(cls,bases,name,dic)


                                     Michele