python - pickle および copy-persistent オブジェクトのクラス?

Question

モジュールで実際にはコピーされない読み取り専用オブジェクトのクラスを作成しようとしていcopyます。プロセス間で転送するためにピクルされると、各プロセスはそのコピーを1つしか保持しません。多くの場合、「新しい」オブジェクトとして渡されます。すでにそのようなものはありますか？

Answer 1

これを実装しようとしました。@Alex Martelli および他の方は、コメントや改善点を教えてください。これは最終的に GitHub で終わると思います。

"""
todo: need to lock library to avoid thread trouble?

todo: need to raise an exception if we're getting pickled with
an old protocol?

todo: make it polite to other classes that use __new__. Therefore, should
probably work not only when there is only one item in the *args passed to new.

"""

import uuid
import weakref

library = weakref.WeakValueDictionary()

class UuidToken(object):
    def __init__(self, uuid):
        self.uuid = uuid


class PersistentReadOnlyObject(object):
    def __new__(cls, *args, **kwargs):
        if len(args)==1 and len(kwargs)==0 and isinstance(args[0], UuidToken):
            received_uuid = args[0].uuid
        else:
            received_uuid = None

        if received_uuid:
            # This section is for when we are called at unpickling time
            thing = library.pop(received_uuid, None)
            if thing:
                thing._PersistentReadOnlyObject__skip_setstate = True
                return thing
            else: # This object does not exist in our library yet; Let's add it
                new_args = args[1:]
                thing = super(PersistentReadOnlyObject, cls).__new__(cls,
                                                                     *new_args,
                                                                     **kwargs)
                thing._PersistentReadOnlyObject__uuid = received_uuid
                library[received_uuid] = thing
                return thing

        else:
            # This section is for when we are called at normal creation time
            thing = super(PersistentReadOnlyObject, cls).__new__(cls, *args,
                                                                 **kwargs)
            new_uuid = uuid.uuid4()
            thing._PersistentReadOnlyObject__uuid = new_uuid
            library[new_uuid] = thing
            return thing

    def __getstate__(self):
        my_dict = dict(self.__dict__)
        del my_dict["_PersistentReadOnlyObject__uuid"]
        return my_dict

    def __getnewargs__(self):
        return (UuidToken(self._PersistentReadOnlyObject__uuid),)

    def __setstate__(self, state):
        if self.__dict__.pop("_PersistentReadOnlyObject__skip_setstate", None):
            return
        else:
            self.__dict__.update(state)

    def __deepcopy__(self, memo):
        return self

    def __copy__(self):
        return self

# --------------------------------------------------------------
"""
From here on it's just testing stuff; will be moved to another file.
"""


def play_around(queue, thing):
    import copy
    queue.put((thing, copy.deepcopy(thing),))

class Booboo(PersistentReadOnlyObject):
    def __init__(self):
        self.number = random.random()

if __name__ == "__main__":

    import multiprocessing
    import random
    import copy

    def same(a, b):
        return (a is b) and (a == b) and (id(a) == id(b)) and \
               (a.number == b.number)

    a = Booboo()
    b = copy.copy(a)
    c = copy.deepcopy(a)
    assert same(a, b) and same(b, c)

    my_queue = multiprocessing.Queue()
    process = multiprocessing.Process(target = play_around,
                                      args=(my_queue, a,))
    process.start()
    process.join()
    things = my_queue.get()
    for thing in things:
        assert same(thing, a) and same(thing, b) and same(thing, c)
    print("all cool!")

Answer 2

レシーバーでキーと値が同じである辞書を単純に使用できます。また、メモリリークを回避するには、WeakKeyDictionaryを使用します。