Simple example of use of __setstate__ and __getstate__

class Foo(object):
    def __init__(self, val=2):
        self.val = val
    def __getstate__(self):
        print ("I'm being picked")
        self.val *= 2
        return self.__dict__

    def __setstate__(self, d):
        print("I'm being unpickled with these values:", d)
        self.__dict__ = d
        self.val *= 3

import pickle
f = Foo()
f_string = pickle.dumps(f) # 带s的,可以理解为string
print(f_string)

f_new = pickle.loads(f_string)
print(f_new)

I'm being picked
b'\x80\x03c__main__\nFoo\nq\x00)\x81q\x01}q\x02X\x03\x00\x00\x00valq\x03K\x04sb.'
I'm being unpickled with these values: {'val': 4}
<__main__.Foo object at 0x0000028927245B70>