def getValue(self, attributeName):
    if hasattr(self, attributeName):
        return getattr(self, attributeName)
    elif attributeName == 'A1':
        v = ... code to get value for A1
        self.A1 = v
        return v
    elif attributeName == 'A2':
        v = ... code to get value for A2
        self.A2 = v
        return v
    ....

class cached_property(object):
    """Define property caching its value on per instance basis.
    Decorator that converts a method with a single self argument into a
    property cached on the instance.
    """
    def __init__(self, method):
        self.method = method

    def __get__(self, instance, type):
        res = instance.__dict__[self.method.__name__] = self.method(instance)
        return res

class Foo:
    def __init__(self):
        # ordinary attributes
        self.B1 = something
        self.B2 = something_else

    @property
    def A1(self):
        try:
            return self._A1
        except AttributeError:
            self._A1 = ....calculate it....
            return self._A1

foo = Foo()
print foo.A1  # attribute calculated when first used
print foo.A1  # this time, the value calculated before is used