在 python 中初始化静态 class 属性

Question

我有以下class

class Test:
    x = None  # this is a static variable common to all object created from this class

    @classmethod
    def initializeX(cls):
        cls.x = 5

请注意 x 在实践中是一个对象，它需要由这个 class 创建的所有对象共有，我不能写例如 x = 5 所以我需要一个函数来初始化它。那么我怎样才能调用只初始化 x 一次而不是为每个创建的对象初始化的函数呢？在 python 中跳过 x = None 并直接在 initializeX(cls) 中定义 x 通常也是好的做法吗？

Answer 1

在 class 构造函数中，您可以编写一个 if 检查以查看 class 属性是否已经创建

if Test.x is None:
  # Do initialization

Answer 2

你有什么理由不能做这样的事情吗？


def _new_x():
    return [1, 2, 3]  # <~~ whatever obj you need to initialize


class Test:
    x = _new_x()


instance_a = Test()
instance_b = Test()

# note they're the same:
assert instance_a.x is instance_b.x

Answer 3

您可以在 class 级别初始化（并设置）它。

class Test:
    x = None  # this is a static variable common to all object created from this class
    @classmethod
    def initializeX(self, cls):
        type(cls).x = 5    # Test.x

c1 = Test()
c2 = Test()

c1.initializeX(c1)
print(c1.x)   # 5
print(c2.x)   # 5

Test.x = 10
print(c1.x)   # 10
print(c2.x)   # 10

输出

在 python 中初始化静态 class 属性

Initialize static class atributes in python

python

class

static-variables