18 组装类举例

MetaClass

from types import MethodType


class A:
    pass


def say(self):
    print("this is say()")


a = A()
a.say = MethodType(say, A)
a.say()

>>>

this is say()

type

# 1. 定义类应该具有的成员函数
def say(self):
    print("this is say()")


def eat(self):
    print("this is eat()")


# 2. 用 type 来创建一个类
A = type("AName", (object,), {"class_say": say, "class_eat": eat})

# 3. 像正常访问一样使用类
a = A()

a.class_say()
a.class_eat()

>>>

this is say()
this is eat()

MetaClass

# 元类写法是固定的，必须继承自 type
# 元类一般命名以 MetaClass 结尾
class ExampleMetaClass(type):
    def __new__(cls, region, gender, attrs):
        print("this is MetaClass")
        attrs['id_num'] = '9527'
        attrs['age'] = "18"
        return type.__new__(cls, region, gender, attrs)


# 元类定义完就可以使用
class Person(object, metaclass=ExampleMetaClass):
    pass


york = Person()
print(york.id_num)

>>>

this is MetaClass
9527