Python: Pickling a dict with some unpicklable items

Question

I have an object gui_project which has an attribute .namespace, which is a namespace dict. (i.e. a dict from strings to objects.)

(This is

Answer 1

One approach would be to inherit from pickle.Pickler, and override the save_dict() method. Copy it from the base class, which reads like this:

def save_dict(self, obj):
    write = self.write

    if self.bin:
        write(EMPTY_DICT)
    else:   # proto 0 -- can't use EMPTY_DICT
        write(MARK + DICT)

    self.memoize(obj)
    self._batch_setitems(obj.iteritems())

However, in the _batch_setitems, pass an iterator that filters out all items that you don't want to be dumped, e.g

def save_dict(self, obj):
    write = self.write

    if self.bin:
        write(EMPTY_DICT)
    else:   # proto 0 -- can't use EMPTY_DICT
        write(MARK + DICT)

    self.memoize(obj)
    self._batch_setitems(item for item in obj.iteritems() 
                         if not isinstance(item[1], bad_type))

As save_dict isn't an official API, you need to check for each new Python version whether this override is still correct.