By looking at the other examples in the howto, I saw there is the same problem in all the definitions in the prompt, and furthermore, we are using a different number of spaces to indent MyClass respect the rest of the classes defined in the prompt. 
There is also a wrong indentation in the StaticMethod definition (no prompt definition):

class StaticMethod(object):
 "Emulate PyStaticMethod_Type() in Objects/funcobject.c"

 def __init__(self, f):
      self.f = f

 def __get__(self, obj, objtype=None):
      return self.f

Applying the py3full.patch, the howto passes all the documentation tests:

$ python -m doctest descriptor.rst | tail -n 1
***Test Failed*** 18 failures.
$ python -m doctest descriptor_modified.rst | tail -n 1
$


My 2 cents