python单例模式的实现

1 线程不安全的单例模式

# -*- coding:utf-8 -*-
from __future__ import unicode_literals

import functools


def singleton(func):
    """线程不安全的单例模式"""

    @functools.wraps(func)
    def wrapper(*args, **kw):
        if not hasattr(func, 'singleton_attr'):
            func.singleton_attr = func(*args, **kw)
        return func.singleton_attr

    return wrapper


if __name__ == '__main__':
    @singleton
    def get_demo_list():
        return [1, 2, 3]


    list_1 = get_demo_list()
    list_2 = get_demo_list()
    assert id(list_1) == id(list_2)

2 线程安全的单例模式

# -*- coding:utf-8 -*-
from __future__ import unicode_literals

import threading


class SingletonMixin(object):
    """
    thread safe singleton base class
    refer: https://gist.github.com/werediver/4396488

    # Based on tornado.ioloop.IOLoop.instance() approach.
    # See https://github.com/facebook/tornado
    """
    __singleton_lock = threading.Lock()
    __singleton_instance = None

    @classmethod
    def instance(cls):
        """

        :rtype: SingletonMixin
        """
        if not cls.__singleton_instance:
            with cls.__singleton_lock:
                if not cls.__singleton_instance:
                    cls.__singleton_instance = cls()
        return cls.__singleton_instance


class SingleDemo(SingletonMixin):
    def __init__(self):
        pass

    @classmethod
    def instance(cls):
        """

        :rtype: SingleDemo
        """
        return super(SingleDemo, cls).instance()


if __name__ == '__main__':
    obj_1 = SingleDemo.instance()
    obj_2 = SingleDemo.instance()

    assert id(obj_1) == id(obj_2)