[Twisted-Python] issues using pb.Copyable

Jean-Paul Calderone exarkun at divmod.com
Fri Oct 27 09:23:07 EDT 2006

On Fri, 27 Oct 2006 00:33:17 -0400, Deepankar Sharma <deepankar.sharma at gmail.com> wrote:
>I am trying to use pb.Copyable to send some python objects back and forth
>between a client and server. I followed the documentation and quickly got
>some simple examples working.
>However i got stuck when i tried sending some python objects which are
>actually wrappers for stuff written in C. Here is an example of what i am
>trying to do
>Class C (Wrapper for a c data structure)
>Class B (inherits from class C and from pb.Copyable)
>I have a lot of wrapper functions which give me instances of Class C. Trying
>to do c_instance.__class__ = B does not work.
>I somehow need to cast those instances into instances of class B so that the
>jellying/unjellying can take place. What does one do in such a situation ?

Instead of subclassing C, write a wrapper for it.  Implement getStateFor on
the wrapper.  For example:

>>> from twisted.spread import pb
>>> class X(object):
...     def __init__(self, y):
...             self.y = y
>>> class Z(pb.Jellyable):
...     def __init__(self, x):
...             self.x = x
...     def getStateFor(self, jellier):
...             return {'y': self.x.y}
>>> pb.jelly(Z(X(10)))
['__main__.Z', ['dictionary', ['y', 10]]]
>>> from twisted.spread import jelly
>>> def unjellyZ(jellier, state):
...     return Z(X(y=pb.unjelly(state[1])['y']))
>>> jelly.setUnjellyableForClass('__main__.Z', unjellyZ)
>>> pb.unjelly(['__main__.Z', ['dictionary', ['y', 10]]]).x.y


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