How to update class attributes with load function

Question

I have a class in which the method save stores the created object to disk using the pickle package:

def save(
        self,
        filepath,
        ):
    #CHECK ATTRIBUTE VALUES
    pickle_out = open(filepath+'.pickle', 'wb')
    pickle.dump(self, pickle_out)
    pickle_out.close()

Similarly, I want to add a load method that loads a pickled file and updates the object with the loaded attributes.

In my load method, I used:

infile = open(filepath,'rb')
self = pickle.load(infile)
infile.close()

However, this does not update the class attributes. How can I write a load method that does update the class variables?

Answer 1

When not using a C extension or slots, class instance data is stored in a dictionary. You could unpickle the class and replace that dictionary.

import pickle

class Foo:

    def __init__(self, val):
        self.val = val

    def save(self, filepath):
        with open(filepath,'wb') as outfile:
            pickle.dump(self, outfile)

    def load(self, filepath):
        with open(filepath,'rb') as infile:
            self.__dict__ = pickle.load(infile).__dict__

f1 = Foo(1)
f1.save("test.pkl")
del f1
f2 = Foo(2)
print(f2.val)
f2.load("test.pkl")
print(f2.val)

It would make sense to pickle only self.__dict__ because that is the unique data of interest.

I don't see any benefit to this over the normal way of using pickle - have regular function or staticmethod load and return the pickled object. That is the intended use of pickle.