Pickles an object containing weak references.

    :param mixed o: Any object

    :rtype str: The pickled object

def pickle_with_weak_refs( o ):
    """
    Pickles an object containing weak references.

    :param mixed o: Any object

    :rtype str: The pickled object
    """
    if isinstance(o, types.GeneratorType):
        o = [i for i in o]
    walk = dict([ (path,val) for path, val in objwalk(o)])
    for path, val in walk.items():
        if len(path) > MAX_DEPTH or is_lambda(val):
            truncate_attr_at_path(o, path)
        if isinstance(val, weakref.ref):
            setattr_at_path( o, path, val() ) # Resolve weak references
    return pickle.dumps(o)