create a weakref:

>>> import dill 
>>> import weakref
>>> class Object:
...   pass
... 
>>> o = Object()
>>> r = weakref.ref(o)  #XXX: type: weakref.ReferenceType

>>> r
<weakref at 0xb12f60; to 'instance' at 0xb23080>
>>> o
<__main__.Object instance at 0xb23080>
>>> r()
<__main__.Object instance at 0xb23080>
>>> r.__call__()
<__main__.Object instance at 0xb23080>
>>> r.__hash__()
11677824
>>> id(o)
11677824


>>> o2 = Object()
>>> r2 = weakref.ref(o2)
>>> del o2

>>> r2
<weakref at 0xb306f0; dead>
>>> r2()
>>> r2.__call__()
>>> r2.__hash__()
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: weak object has gone away


>>> o3 = Object()
>>> r3 = weakref.proxy(o3)  #XXX: type: weakref.ProxyType

>>> r3
<weakproxy at 0x85b10 to instance at 0x8d530>
>>> o3
<__main__.Object instance at 0x8d530>
>>> r3.__class__
<class __main__.Object at 0x6aa50>
>>> o3.__class__
<class __main__.Object at 0x6aa50>

>>> del o3
>>> r3
<weakproxy at 0x85b10 to NoneType at 0x4f1aa0>
>>> r3.__class__
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
ReferenceError: weakly-referenced object no longer exists


>>> class Object2:
...   def __call__(self):
...     pass
... 
>>> oo = Object2()
>>> oo
<__main__.Object instance at 0x8ca30>
>>> oo()
>>> rr = weakref.proxy(oo)  #XXX: type: weakref.CallableProxyType
>>> rr
<weakproxy at 0x82930 to instance at 0x8ca30>
>>> rr()
>>> rr.__call__
<bound method Object.__call__ of <__main__.Object instance at 0x8ca30>>
>>> rr.__call__()
>>> 


########################################
approach to pickling weakrefs:

*) register the weakref types ?  (see line ~228 of dill.py)

*) use hash to create hard copy of ref object
   then upon unpickle, create new weakref

*) propose that pickling a weakref will always provide a dead reference
   unless the reference object is pickled along with the weakref

########################################
pickling generators:

*) need to avoid the "new" method for FrameTypes...
don't see how to do that, without going into C to get the GID Thread.

*) currently inspecting: Objects/object.c Objects/dictobject.c Objects/genobject.c Objects/frameobject.c Python/pystate.c Python/thread.c Python/pythonrun.c 

*) the package "generator_tools" may have the answer.

########################################