Question

New to python…
I have the following class Key, that extends dict:

class Key( dict ):

    def __init__( self ):
        self = { some dictionary stuff... }

    def __getstate__(self):
        state = self.__dict__.copy()
        return state

    def __setstate__(self, state):
        self.__dict__.update( state )

I want to save an instance of the class with its data using pickle.dump and then retrieve the data using pickle.load. I understand that I am supposed to somehow change the getstate and the setstate, however, am not entirely clear on how I am supposed to do that… any help would be greatly appreciated!

Answer 1

I wrote a subclass of dict that does this here it is.

class AttrDict(dict):
    """A dictionary with attribute-style access. It maps attribute access to
    the real dictionary.  """
    def __init__(self, *args, **kwargs):
        dict.__init__(self, *args, **kwargs)

    def __getstate__(self):
        return self.__dict__.items()

    def __setstate__(self, items):
        for key, val in items:
            self.__dict__[key] = val

    def __repr__(self):
        return "%s(%s)" % (self.__class__.__name__, dict.__repr__(self))

    def __setitem__(self, key, value):
        return super(AttrDict, self).__setitem__(key, value)

    def __getitem__(self, name):
        return super(AttrDict, self).__getitem__(name)

    def __delitem__(self, name):
        return super(AttrDict, self).__delitem__(name)

    __getattr__ = __getitem__
    __setattr__ = __setitem__

    def copy(self):
        return AttrDict(self)

It basically converts the state to a basic tuple, and takes that back again to unpickle.

But be aware that you have to have to original source file available to unpickle. The pickling does not actually save the class itself, only the instance state. Python will need the original class definition to re-create from.