python中单例的实现

单例的解释

单例模式是一种常用的软件设计模式。在它的核心结构中只包含一个被称为单例类的特殊类。通过单例模式可以保证系统中一个类只有一个实例而且该实例易于外界访问，从而方便对实例个数的控制并节约系统资源。如果希望在系统中某个类的对象只能存在一个，单例模式是最好的解决方案。

 

import作为python的模块是天然的单例模式

可以使用模块创建单例模式，然后在其他模块中导入该单例，这个需要所有人遵守导入规则，不然就没法实现单例了

# use_module.py
class SingleTon(object):

    def __init__(self, val):
        self.val = val

single = SingleTon(2)

# test_module.py
from use_module import single

a = single
b = single
print a.val, b.val
print a is b
a.val = 233
print a.val, b.val

使用__new__实现单例模式

class SingleTon(object):
    _instance = {}

    def __new__(cls, *args, **kwargs):
        if cls not in cls._instance:
            cls._instance[cls] = super(SingleTon, cls).__new__(cls, *args, **kwargs)
        # print cls._instance
        return cls._instance[cls]


class MyClass(SingleTon):
    class_val = 22

    def __init__(self, val):
        self.val = val

    def obj_fun(self):
        print self.val, 'obj_fun'

    @staticmethod
    def static_fun():
        print 'staticmethod'

    @classmethod
    def class_fun(cls):
        print cls.class_val, 'classmethod'


if __name__ == '__main__':
    a = MyClass(1)
    b = MyClass(2)
    print a is b   # True
    print id(a), id(b)  # 4367665424 4367665424
    # 类型验证
    print type(a)  # <class '__main__.MyClass'>
    print type(b)  # <class '__main__.MyClass'>

 

装饰器实现 

from functools import wraps


def single_ton(cls):
    _instance = {}

    @wraps(cls)
    def single(*args, **kwargs):
        if cls not in _instance:
            _instance[cls] = cls(*args, **kwargs)
        return _instance[cls]
    return single


@single_ton
class SingleTon(object):
    val = 123

    def __init__(self, a):
        self.a = a

if __name__ == '__main__':
    s = SingleTon(1)
    t = SingleTon(2)
    print s is t
    print s.a, t.a
    print s.val, t.val