How do you pass multiple arguments to __setstate__?

Question

I am doing deepcopy on a class I designed, which has multiple lists as attributes to it. With a single list, this is solvable by overriding getstate to return that list, and setstate to set that list, but setstate seems unable to take multiple parameters.

How is this accomplished?

Answer 1

You can have __getstate__ return (and __setstate__ accept) a list of lists, or a dict (if you implement __getstate__ and __setstate__, __getstate__ doesn't have to return a dict)

import pickle

class Example:
    def __init__(self):
        self.list1 = [1]
        self.list2 = [2]

    def __getstate__(self):
        return {'list1': self.list1, 'list2': self.list2}

    def __setstate__(self, state):
        self.list1 = state['list1']
        self.list2 = state['list2']

ex = Example()
s = pickle.dumps(ex)
ex2 = pickle.loads(s)
print ex.list1, ex.list2

This is just a demo. You really don't even need to override pickle's default behavior for a simple case like this.