Object caching metaclass

gistfile1.py

# Metaclass for caching objects based on constructor argument

class Cached(type):
    def __new__(cls, name, bases, dct):
        dct['_cache'] = {}
        return super(Cached, cls).__new__(cls, name, bases, dct)
    def __call__(cls, a):
        try:
            return cls._cache[a]
        except KeyError:
            o = super(Cached, cls).__call__(a)
            cls._cache[a] = o
            return o
        

class C(object):
    __metaclass__ = Cached

    def __init__(self, i):
        print "C", i
        self.i = i

class D(object):
    __metaclass__ = Cached

    def __init__(self, i):
        print "D", i
        self.i = i

a = C(1)
b = C(2)
c = C(1)
d = D(1)

print a is c
print a is d
print C._cache
print D._cache