root/supersingleton/single.py

class A(object):

    exporting_methods= ['seta','geta']
    @staticmethod
    def _ready():
        return getattr(A, '_the_instance', None)
    
    def __new__(cls, *p, **k):

        i= A._ready()
        if i is None:
            A._the_instance= object.__new__(A)
            if cls is A:
                return A._the_instance
            A.__init__(A._the_instance)
            i= A._the_instance

        o= object.__new__(cls)

        for attr_name in A.exporting_methods:
            setattr(o, attr_name, getattr(i, attr_name))

        return o

    def __init__(self, a=1):
        self.a=a

    def geta(self):
        print self.a

    def seta(self, v):
        self.a= v

    def prima(self):
        print 'prima'
        self.prima= self.dopo

    def dopo(self):
        print 'dopo'

class B(A):
    def __init__(self, x):
        self.x= x

class C(A):
    def __init__(self, z):
        self.z= z

# se commenti la seguente, AA.a sara' 1:
# i valori di __init__ di A non possono essere espressi.
#a=A(1999)

#b= B(77)
#n= B(66)
#b.geta()
#n.seta(666)
#b.geta()


class AA:
    def __init__(self):
        pass
    def az(self):
        self.pippo=1

class BB:
    def __init__(self):
        self.medium= AA()