ROType.py

class ROType(type):
    def __new__(mcl, classname, bases, classdict):
        class UniqueROType (mcl):
            pass

        def getAttrFromMetaclass(attr):
            return lambda cls: getattr(cls.__metaclass__, attr, None)
        
        for attr, value in classdict.items():
            if not hasattr(value, '__call__') and attr.startswith('_') and not attr.startswith('__'):
                # Store the private value on the metaclass.
                setattr(mcl, attr, value)

                # Create a property whose getter queries the attr from the metaclass.
                p = property(getAttrFromMetaclass(attr))

                # Add the property to our empty metaclass so the correct property
                # behavior is generated on the class.
                setattr(UniqueROType, attr[1:], p)

                # Expose the new 'public' read-only property on the class.
                classdict[attr[1:]] = p

                # Remove the private value from the class.
                classdict.pop(attr, None)
                
        return type.__new__(UniqueROType, classname, bases, classdict)


#
# EXAMPLES
#

class Foo(object):
    __metaclass__ = ROType
    foo = 0
    _bar = 1
    _baz = 2

class Test(object):
    __metaclass__ = ROType
    foo = 'hello'
    _bar = 'world'
    _baz = 'sam'