Missing attribute after using multiprocessing Queue about qubovert

[jtiosue]

Hi, thanks for raising the issue! I'm afraid I'm not very familiar with the multiprocessing package or Queue object. Have you been able to reproduce this error in another way?

[smuecke]

This seems to be an issue with serialization, as I was able to reproduce it with pickle:

import pickle
from qubovert import PCBO

pcbo = PCBO({(0, 1): -5}) # error happens only when instance is not empty
data = pickle.dumps(pcbo)
pcbo_ = pickle.loads(data) # AttributeError occurs here

The clean solution will probably be to implement the __getstate__() and __setstate__() methods for all instances of PCBO, QUBO etc., which store and restore the object states manually. I think attributes like _degree starting with an underscore are problematic for serialization, because Python renames such attributes in subclasses.
Another solution might be to just rename attributes starting with _ to something without underscore.

Best regards ;)