raises_error.py

import pickle
from django.utils.functional import SimpleLazyObject


class FooBase(object):
    def __reduce__(self):
        self.__dict__['_version'] = 1
        return super(FooBase, self).__reduce__()


class Foo(FooBase):
    def __init__(self, foobase):
        self.__dict__ = foobase.__dict__
        self._foo = foobase

lazy_foo = SimpleLazyObject(lambda: Foo(FooBase()))
print pickle.dumps(lazy_foo) # raises an error

raises_warning.py

# run in a ./manage.py shell
import pickle
from django.contrib.auth.models import User #any model will do
from django.utils.functional import SimpleLazyObject

user = User.objects.get(username='benkraft')
lazy_user = SimpleLazyObject(lambda: user)
pickle.loads(pickle.dumps(lazy_user)) # warns

simpler_error.py

import pickle
from django.utils.functional import SimpleLazyObject


class Foo(object):
    def __reduce__(self):
        self.__dict__['_version'] = 1
        return super(Foo, self).__reduce__()

    def __init__(self):
        self._foo = self

lazy_foo = SimpleLazyObject(lambda: Foo())
print pickle.dumps(lazy_foo) # raises an error