[Numpy-discussion] Possible to pickle new state in NDArray subclasses?

Stuart Reynolds stuart at stuartreynolds.net
Wed Dec 14 14:45:07 EST 2016

I'm trying to subclass an NDArray as shown here:

My problem is that when I save the new class' state with pickle, the new
attributes are lost. I don't seem to be able to override __getstate__ or
__setstate__ to achieve this?

Is it possible to allow new state to serialized when overriding an NDArray?

In my example below, __setstate__ gets called by pickle but not
In the final line, a RealisticInfoArray has been deserialized, but it has
no .info attribute.


import cPickle as pickle
import numpy as np

class RealisticInfoArray(np.ndarray):
    def __new__(cls, arr, info):
        obj = np.asarray(arr).view(cls)
        obj.info = info
        return obj

    def __array_finalize__(self, obj):
        if obj is None: return
        self.info = getattr(obj,"info",None)

    def __setstate__(self, *args):
        print "SET"
        return np.ndarray.__setstate__(self,*args)

    def __getstate__(self):
        print "GET"
        assert False, "EXPLODE"
        return np.ndarray.__getstate__(self)

arr = np.zeros((2,3), int)
arr = RealisticInfoArray(arr, "blarg")
print arr.info
arr2 = pickle.loads(pickle.dumps(arr))
print arr2.info  # no .info attribute!
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