Question

Assume I have a class A and a class B that is derived from A. I want to pickle/unpickle an instance of class B. Both A and B define the __getstate__/__setstate__ methods (Let’s assume A and B are complex, which makes the use of __getstate__ and __setstate__ necessary). How should B call the __getstate__/__setstate__ methods of A? My current, but perhaps not the ‘right’ approach:

class A(object):
    def __init__():
        self.value=1
    def __getstate__(self):
        return (self.value)
    def __setstate__(self, state):
        (self.value) = state

class B(A):
    def __init__():
        self.anothervalue=2
    def __getstate__(self):
        return (A.__getstate__(self), self.anothervalue)
    def __setstate__(self, state):
        superstate, self.anothervalue = state
        A.__setstate__(self, superstate)

Answer 1

I would use super(B,self) to get instances of B to call the methods of A:

import cPickle
class A(object):
    def __init__(self):
        self.value=1
    def __getstate__(self):
        return self.value
    def __setstate__(self, state):
        self.value = state

class B(A):
    def __init__(self):
        super(B,self).__init__()
        self.anothervalue=2
    def __getstate__(self):
        return (super(B,self).__getstate__(), self.anothervalue)
    def __setstate__(self, state):
        superstate, self.anothervalue = state
        super(B,self).__setstate__(superstate)

b=B()
with open('a','w') as f:
    cPickle.dump(b,f)


with open('a','r') as f:
    c=cPickle.load(f)
print(b.value)
print(b.anothervalue)

See this article for more info on method resolution order (MRO) and super.