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直接上代码

元类

metaclass


class MyType(type):
    def __init__(self, *args, **kwargs):
        print("MyType.__init__")
        super().__init__(*args, **kwargs)

    def __new__(cls, *args, **kwargs):
        print("MyType.__new__")
        new_cls = super().__new__(cls, *args, **kwargs)
        print(new_cls)
        return new_cls

    def __call__(self, *args, **kwargs):
        """python实例化一个类时,先调用__new__后调用__init__的原因"""
        print("MyType.__call__")
        empty_obj = self.__new__(self)
        self.__init__(empty_obj, *args, **kwargs)
        return empty_obj

class Foo(metaclass=MyType):  # Foo是MyType的对象
    def __init__(self, name):
        print("Foo.__init__")
        self.name = name

class Foo2(Foo):  # 这个类也是有MyType创建的
	pass

if __name__ == "__main__":
    # 实例化一个类对象时, 调用的是该类的元类的__call__
    foo = Foo("alex")  
    print(foo.name)

元类实现单例模式

元类中的其它参数

class Spam(metaclass=MyMeta, debug=True, synchronize=True):
    pass

https://python3-cookbook.readthedocs.io/zh_CN/latest/c09/p15_define_metaclass_that_takes_optional_arguments.html

装饰器

decorator


装饰方法

import time

def decorator(function):
    def wrapper(*args, **kwargs):
        start_time = time.time()
        result = function(*args, **kwargs)
        end_time = time.time()
        print("use time:", end_time - start_time)
        return result
    return wrapper


@decorator
def func(sleep_time):
    time.sleep(sleep_time)
    return 0

if __name__ == "__main__":
    print("func: ", func)
    # func:  <function decorator.<locals>.wrapper>
    ret = func(1)
    """
    使用装饰器装饰后, 调用func()实际上是调用 wrapper()
    """
    print(ret)

装饰类

def Domain(domain):
    print("enter decorater, domain=", domain)
    print("dir(domain)=", dir(domain))

    def wrapper(cls):
        print("enter wrapper, cls=", cls)
        cls.num_of_animals = 10
        cls.domain = domain
        cls.insert = MysqlMapper.insert
        print("类名", cls.__name__, dir(cls.__class__))
        print("dir(cls)=", dir(cls))
        return cls

    return wrapper


@Domain(Animal)
class AnimalDao(BaseMapper):
    pass