Multiprocessing, shared memory vs. pickled copies

Robert Kern robert.kern at
Thu Apr 7 13:44:05 EDT 2011

On 4/7/11 1:40 AM, John Ladasky wrote:

> On Apr 5, 10:43 am, Philip Semanchuk<phi... at>  wrote:

>> And as Robert Kern pointed out, numpy arrays are also pickle-able.
> OK, but SUBCLASSES of numpy.ndarray are not, in my hands, pickling as
> I would expect.  I already have lots of code that is based on such
> subclasses, and they do everything I want EXCEPT pickle correctly.  I
> may have to direct this line of questions to the numpy discussion
> group after all.

Define the __reduce_ex__() method, not __getstate__(), __setstate__().

ndarrays are extension types, so they use that mechanism.

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

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