Exclude object's field from pickling in python

Question

I would like to avoid pickling of certain fields in an instance of a class. Currently, before pickling I just set those fields to None, but I wonder whether there\'s more el

Answer 1

Pickling uses the object's __getstate__ and __setstate__ methods; you can override them and ignore the fields you want.

# foo.py
class Foo:
    def __init__(self):
        self.bar = 1
        self.baz = 2

    def __getstate__(self):
        state = self.__dict__.copy()
        # Don't pickle baz
        del state["baz"]
        return state

    def __setstate__(self, state):
        self.__dict__.update(state)
        # Add baz back since it doesn't exist in the pickle
        self.baz = 0

# main.py
import pickle

from foo import Foo


foo = Foo()
print(f"Foo bar: {foo.bar} baz: {foo.baz}")

new_foo = pickle.loads(pickle.dumps(foo))
print(f"New bar: {new_foo.bar} baz: {new_foo.baz}")

Output:

Foo bar: 1 baz: 2
New bar: 1 baz: 0

You can find another example here: https://docs.python.org/3/library/pickle.html#handling-stateful-objects