python - Why am I getting "NameError: global name 'open' is not defined" in __del__?

Question

I'm getting a NameError in the __del__ function of a class. I do not understand why 'open' is not accessible inside the function __del__. I am using Python 3.4.0

Python Code:

class Contoller:

    ...

    def __del__(self):
        store = {}
        ...
        pickle.dump(store, open('data.p', 'wb'))    

class MyWindow(Gtk.Window):

    def __init__(self):
        ...
        self.controller = Contoller(self)
        ...
        self.connect("delete-event", self.quit)
        ...

    ...

    def quit(self, widget, event):
        del self.controller
        Gtk.main_quit()

Error Message:

Traceback (most recent call last):
  File "main.py", line 69, in __del__
NameError: name 'open' is not defined

Answer 1

user3595184's code used to work until Python 3.4. I know because I've just run into the same issue, calling open() within __del__. Apparently built-in functions no longer work, because of a change in when __del__ is run as the interpreter shuts down.

UPDATE: See https://docs.python.org/3/library/weakref.html, especially the section on finalizers. I have several classes that encapsulate access to resources that had __del__() methods to unlock or clean up as soon as the application would exit, for any reason. Catching all exceptions or exits at the application level and explicitly calling cleanup methods is inconvenient and bug-prone. I'll try using a local finalizer instead.

UPDATE: I'm having better luck with __enter__() and __exit__(), putting the top-level object in a with clause. It appears at least the __exit__() gets called no matter how, so I can call the cleanup methods (__exit__()'s themselves) of all subordinate objects. That's working for me.