pickling instances of metaclass generated classes

[Robert Kern]

On 12/29/11 9:55 AM, lars van gemerden wrote:
> Hello,
>
> Can someone help me with the following:
>
> I am using metaclasses to make classes and these classes to make
> instances. Now I want to use multiprocessing, which needs to pickle
> these instances.
>
> Pickle cannot find the class definitions of the instances. I am trying
> to add a line to the __new__ of the metaclass to add the new class
> under the right name in the right module/place, so pickle can find
> it.
>
> Is this the right approach? Can anyone explain to me where/how to add
> these classes for pickle to find and maybe why?

Can you post some code (preferably pared down to a minimal example that fails)? 
I'm not really clear on what you are doing. I would expect that a class defined 
by a class statement would usually work fine unless if the metaclass is doing 
something particularly weird to it.

In any case, you can probably just explicitly register a reduction function for 
each type using copy_reg.pickle():

http://docs.python.org/library/copy_reg

-- 
Robert Kern

"I have come to believe that the whole world is an enigma, a harmless enigma
  that is made terrible by our own mad attempt to interpret it as though it had
  an underlying truth."
   -- Umberto Eco