descriptor.py

class via_data:
    def __init__(self, name=None):
        # name can be None for python 3.6
        self.name = name
    def __get__(self, instance, owner):
        if instance is not None:
            assert self.name is not None, 'name not specified'
            return instance.data[self.name]
        return self
    def __set_name__(self, owner, name):
        # only called for python 3.6
        self.name = name


class Foo:
    def __init__(self):
        self.data = {}
        self.data['x'] = 1
        self.data['y'] = 2
        self.data['z'] = 3
    x = via_data()
    y = via_data()
    z = via_data('z')

if __name__ == '__main__':
    foo = Foo()
    print('x', foo.x)
    print('y', foo.y)
    print('z', foo.z)