ispicklable() --> bool, possible?

[Gerrit Holl]

Hi,

I am currently using the following code to check whether an object is
picklable or not:

_canpickle = (NoneType, bool, int, long, float, complex, basestring, FunctionType, ClassType)
_cantpickle = (GeneratorType, pygame.sprite.Group, pygame.sprite.GroupSingle, pygame.sprite.Sprite, pygame.rect.Rect, pygame.Surface)
def picklable(obj):
    for inst in _canpickle:
        if isinstance(obj, inst):
            return True
    for inst in _cantpickle:
        if isinstance(obj, inst):
            return False
    if isinstance(obj, dict):
        obj = obj.values()
    if isinstance(obj, list) or isinstance(obj, tuple):
        for subobj in obj:
            if not picklable(subobj):
                return False
        return True
    debug("unknown", obj)
    try:
        cPickle.dumps(obj)
    except (TypeError, cPickle.UnpickleableError):
        return False
    else:
        return True

However, this has problems. For instance, a list can be recursive,
which causes this function to loop. An obj can contain itself, and
if the obj's __getstate__ calls picklable, this function loops. The
latter was true in my case, because I'm using my function to check
whether I should do a certain operation on my instances' __data__
or not dependant on among others the result of picklable().

Is there a better, clean way to check whether an object is picklable
or not? I have not found any such function is the pickle library.
Nor have I found it in the standard library. Not have I found it on
the internet. Nor have I found it in the archives. Nor have I found
out whether it is theoratically possible. Nor have I found out whether
to spell picklable with or without the trailing 'e' of pickle (i.e.
pickleable or picklable).

yours,
Gerrit.

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