Save pipeline "can't pickle abc_data objects" error

[luizfelippesr]

As first reported by @ashley-stock, trying to save a Pipeline object which includes FieldFactory classes defined within the running notebook leads to error. A minimal version of such error can be seen below:

import imagine as img
import imagine_datasets as img_data

original_bregLSA = img.fields.hamx.BregLSAFactory()

class LocalBregLSAFactory(img.fields.FieldFactory):
    """This is fully equivalent to BregLSAFactory!"""
    FIELD_CLASS = original_bregLSA.field_class
    DEFAULT_PARAMETERS = original_bregLSA.default_parameters
    PRIORS = original_bregLSA.priors

factory_list = [LocalBregLSAFactory()]
measurement = img.observables.Measurements(img_data.HEALPix.fd.Oppermann2012(Nside=2))
simulator = img.simulators.Hammurabi(measurement)
likelihood = img.likelihoods.EnsembleLikelihood(measurement)
pipeline = img.pipelines.MultinestPipeline(simulator=simulator,
                                           likelihood=likelihood, 
                                           factory_list=factory_list)
pipeline.save()

this leads to

TypeError: can't pickle _abc_data objects

Interestingly, if one replaces LocalBregLSAFactory() by original_bregLSA, everything works normally.

The error is actually a problem with dill and the way it serializes objects defined in __main__. We can get the same error by simply doing (using the same definitions as above):

with open('/tmp/test.pkl', 'wb') as f:
    dill.dump(LocalBregLSAFactory(), f)

Issue uqfoundation/dill#332 is related to this.