Issue 20836: Pickle Nonetype - Python tracker (original) (raw)

This simple code works, but I have two 'import pickle' lines.

The none working code has one 'import pickle' outside the class definition. This raises a Nonetype error in the pickle module, in the del method. I'd like to know why and I think it's a bug, or is it?

class Login(): users = {}

def __init__(self):
    try:
        with open('user.data','rb') as f:
            import pickle
            self.users = pickle.load(f)

print('init: {}'.format(self.users))

    except Exception:
        #'user.data' file doesn't exist
        pass

def __del__(self):
    try:
        with open('user.data','wb') as f:

print('del: {}'.format(self.users))

print(type(self.users))

print(type(f))

            import pickle
            pickle.dump(self.users, f, pickle.HIGHEST_PROTOCOL)
    except Exception as e:
        print('__del__ Shit happened: {}'.format(e))

Before python 3.4, del methods are problematic. During interpreter shutdown various module attributes get set to None, which is probably what is triggering the error.

It is unlikely there is a Python bug here: it is a known and documented issue that module attributes can disappear (get set to None) before del methods are run, if objects are not GCed before interpreter shutdown starts. (Pre 3.4. In 3.4 this situation is much improved.)