原来Python类还有这么多花样

Posted 2021-01-12 知我几分

"""metaclass的作用是指定当前类由谁来创建"""


# 第一种创建类的方式
class Foo(object):
    name = "小强"     # 类的静态字段

    def func(self):
        return 666


val = Foo()
print(val.name)

# 第二种创建类的方式
Foo1 = type("Foo", (object,), {"name": "小强", "func": lambda self: 666})

val1 = Foo1()
print(val1.name)


# 2.自定义type
class YouType(type):
    pass


class Foo2(object, metaclass=YouType):    # metaclass指定当前继承类
    name = "小老鼠"

    def func(self):
        return "猫不抓"


val2 = Foo2()
print(val2.name)

Foo3 = YouType("Foo", (object,), {"name": "小老鼠", "func": lambda self: "猫不抓"})

val3 = Foo3()
print(val3.name)


# 3.metaclass
class MyType(type):

    def __init__(self, *args, **kwargs):
        super(MyType, self).__init__(*args, **kwargs)

    def __call__(cls, *args, **kwargs):
        obj = cls.__new__(cls)
        cls.__init__(obj, *args, **kwargs)
        return obj


class Foo4(object, metaclass=MyType):
    name = "旺财"

    def __init__(self):
        pass

    def __new__(cls, *args, **kwargs):
        return object.__new__(cls)

    def func(self):
        return 666


# Foo4是MyType的一个对象
obj = Foo4()
print(obj.name)

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