>>> from persistent import Persistent
>>> class D(object):
...     """
...     """
...
>>> class S(object):
...     __slots__ = ['a']
...
>>> D.__dictoffset__
8
>>> S.__dictoffset__
0
>>> Persistent.__dictoffset__
0
>>> S.__slots__
['a']
>>> Persistent.__slots__
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
AttributeError: type object 'persistent.Persistent' has no attribute '__slots__'

>>> x = Persistent()
>>> x.bar = 1
  Traceback (most recent call last):
    ...
  AttributeError: 'Persistent' object has no attribute 'bar'

>>> x = Persistent()
>>> print x.__getstate__()
None

"If the object has assigned slots, then a two-element tuple is returned.  \n"
"The first element is either None or a copy of the instance dictionary, \n"
"The second element is a dictionary with items \n"
"for each of the assigned slots.\n"

>>> class A(object):
...     __slots__ = ['a']
...
>>> del A.__slots__
>>> A.__slots__
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
AttributeError: type object 'A' has no attribute '__slots__'
>>> obj = A()
>>> obj.a = 10
>>> obj.b = 15
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
AttributeError: 'A' object has no attribute 'b'
>>> A.__dictoffset__
0