Known Bug in Python Pickle?

Question

Given the following code:

import pickle

class Test:
    d = {}    

    def func(self):
        self.d['x'] = 'y'

test = Test()
test.func()
pickle.dump(test, open('test.p', 'wb'))

%reset

import pickle
class Test:
    d = {}    

    def func(self):
        self.d['x'] = 'y'


print(pickle.load(open('test.p', 'rb')).d)

I would expect the output

y
y

However, the actual output is

y
{}

Is this a known bug or am I misunderstanding something?

I am using Miniconda Python 3.5.2 on Windows.

Answer 1

From the pickle documentation

... when class instances are pickled, their class’s code and data are not pickled along with them. Only the instance data are pickled.

The behavior you see is documented and not in error.