python - 为类动态添加类方法

Question

我有以下片段:

FEED_TYPES = [
    ('fan_mail',     'Fan Mail'),
    ('review',       'Review'),
    ('tip',          'Tip'),
    ('fan_user',     'Fan User'),
    ('fan_song',     'Fan Song'),
    ('fan_album',    'Fan Album'),
    ('played_song',  'Played Song'),
    ('played_album', 'Played Album'),
    ('played_radio', 'Played Radio'),
    ('new_event',    'New Event'),
]

class Feed:
    @classmethod
    def do_create(cls, **kwargs):
        print kwargs

    @classmethod
    def create(cls, type, **kwargs):
        kwargs['feed_type'] = type
        cls.do_create(**kwargs)

for type_tuple in FEED_TYPES:
    type, name = type_tuple

    def notify(self, **kwargs):
        print "notifying %s" % type
        self.create(type, **kwargs)

    notify.__name__ = "notify_%s" % type
    setattr(Feed, notify.__name__, classmethod(notify))

Feed.create("FanMail", to_profile="Gerson", from_profile="Felipe")
Feed.notify_fan_mail(to_profile="Gerson2", from_profile="Felipe2")

想法是为每种提要类型动态创建一个类方法(如 notify_fan_mail)。它工作得很好，唯一的问题是 print 语句总是打印“notifying new_event”，不管我调用什么方法(notify_new_mail、notify_review 等)。

我意识到这是因为它使用了分配给类型的最后一个值。我的问题是:如何动态创建方法来为 type 使用正确的值？

此外，如果我在 Python 文件中有这个确切的代码，那么这是向 Feed 类添加方法的正确方法，还是有更优雅的方法？

Answer 1

使用闭包来保存 kind 的值:

for type_tuple in FEED_TYPES:
    kind, name = type_tuple
    def make_notify(kind):
        def notify(self, **kwargs):
            print "notifying %s" % kind
            self.create(kind, **kwargs)
        return notify
    notify = make_notify(kind)
    notify.__name__ = "notify_%s" % kind
    setattr(cls, notify.__name__, classmethod(notify))

顺便说一下，不要使用 type 作为变量名，因为它会隐藏同名的内置函数。

---

修改 Feed 的一种更优雅的方法是创建类装饰器。这更清楚地表明您有代码修改了 Feed 的原始定义。

FEED_TYPES = [
    ('fan_mail',     'Fan Mail'),
    ('review',       'Review'),
    ('tip',          'Tip'),
    ('fan_user',     'Fan User'),
    ('fan_song',     'Fan Song'),
    ('fan_album',    'Fan Album'),
    ('played_song',  'Played Song'),
    ('played_album', 'Played Album'),
    ('played_radio', 'Played Radio'),
    ('new_event',    'New Event'),
]

def add_feed_types(cls):
    for type_tuple in FEED_TYPES:
        kind, name = type_tuple
        def make_notify(kind):
            def notify(self, **kwargs):
                print "notifying %s" % kind
                self.create(kind, **kwargs)
            return notify
        notify = make_notify(kind)
        notify.__name__ = "notify_%s" % kind
        setattr(cls, notify.__name__, classmethod(notify))
    return cls

@add_feed_types
class Feed:
    @classmethod
    def do_create(cls, **kwargs):
        print kwargs

    @classmethod
    def create(cls, kind, **kwargs):
        kwargs['feed_type'] = kind
        cls.do_create(**kwargs)


Feed.create("FanMail", to_profile="Gerson", from_profile="Felipe")
Feed.notify_fan_mail(to_profile="Gerson2", from_profile="Felipe2")