Python-实现单例的多种方式（类、函数、自定义）

 

"""
单例类
方法1：外部函数实现
方法2：外部类数实现
方法3：__new__内置函数实现

__new__函数：在实例化开始时，在调用初始化__init__() 方法之前， 首先调用 __new__() 方法
"""

def singleton(cls):
    """
    修饰类（实现类单例）
    @param cls:
    """
    instances = {}
    def inner(*args, **kwargs):
        if cls not in instances:
            instances[cls] = cls(*args,**kwargs)
        return instances[cls]
    return inner


#修饰类（实现类单例）
class Singleton(object):
    def __init__(self, cls):
        self._cls = cls
        self._instance = {}
    def __call__(self):
        if self._cls not in self._instance:
            self._instance[self._cls] = self._cls()
        return self._instance[self._cls]


#内置函数（实现类单例）
class Singleton1(object):
    def __new__(cls, *args, **kwargs):
        if not hasattr(cls, '_inst'):
            cls._inst = super(Singleton1, cls).__new__(cls)
        return cls._inst

#内置函数（实现类单例）
class Singleton2(object):
    def __new__(cls, *args, **kwargs):
        if not hasattr(cls, '_inst'):
            cls._inst = object.__new__(cls)
        return cls._inst


#自定义单列
class Person(object):
    def __new__(cls, name, age):
        if 0 < age < 100:
            return object.__new__(cls)
        else:
            return None

    def __init__(self, name, age):
        self.name = name
        self.age = age

    def __str__(self):
        return f'{self.__class__.__name__}{self.__dict__}'


if __name__ == '__main__':
    s1 = Singleton1()
    s2 = Singleton1()
    print(s1)
    print(s2)

    p1 = Person('Tom', 10)
    p2 = Person('Mike', 200)
    print(p1)
    print(p2)

 

 

"""
单例函数
"""

token=None
def get_token():
    global token
    if token is None:
        token='123'
    return token

if __name__ == '__main__':

    print(get_token())
    print(get_token())