python - 在 python 中使用 lambda 或 helper 方法来避免 for 循环重复

Question

我有以下简单的类，想知道是否有一种简单的方法来使用 lambda、decorator 或 helper 方法，等等...以避免 CODENAMES 和 ALL_DEFAULTS 中的每个方法中出现重复的 for 循环?

class classproperty(object):
    """
    When used to decorate a method in a class, that method will behave
    like as a class property.
    """
    def __init__(self, f):
        # f - the func that's being decorated
        self.f = f

    def __get__(self, obj, cls):
        # call the func on the class
        return self.f(cls)

class PermissionInfo(object):

    MODELS = ['ticket', 'person', 'role']
    PERMS = ['view', 'add', 'change', 'delete']

    @classproperty
    def CODENAMES(cls):
        codenames = []
        for p in cls.PERMS:
            for m in cls.MODELS:
                codenames.append('{}_{}'.format(p, m))
        return codenames

    @classproperty
    def ALL_DEFAULTS(cls):
        ret = {}

        for p in cls.PERMS:
            for m in cls.MODELS:
                ret["{}_{}".format(p, m)] = False

        return ret

重复的for循环是每个方法的这一部分:

# ...
for p in cls.PERMS:
    for m in cls.MODELS:
#...

Answer 1

你可以使用 itertools.product在辅助方法中生成名称:

from itertools import product

def names(cls):
    yield from ('_'.join(x) for x in product(cls.PERMS, cls.MODELS))

然后你可以改变你的类来使用它:

@classproperty
def CODENAMES(cls):
    return list(names(cls))

@classproperty
def ALL_DEFAULTS(cls):
    return dict.fromkeys(names(cls), False)