Python descriptors do not work in Python 2.7

This code produces a different output in Python 2and Python 3.

class Descriptor(object):
    def __get__(self, instance, owner):
        print('read')
        return 1

    def __set__(self, instance, value):
        print('write')

    def __delete__(self, instance):
        print('del')

class C():
    a = Descriptor()

c = C()                                
c.a                                    
c.a = 3
del c.a
c.a

print('finished')

Output for Python 2:

read
read
finished

For Python 3, this is:

read
write
del
read
finished

Why does this work? How do descriptors Python 2differ from descriptors Python 3?

This doesn't make sense either, because http://docs.python.org/release/3.0.1/reference/datamodel.html#invoking-descriptors clearly describes the same thing as http://docs.python.org /reference/datamodel.html#invoking-descriptors

(This is the documentation for Python 2.7and Python 3.0.)