Python的單例模式

#!/usr/bin/python
#coding: UTF-8
"""
@author: CaiKnife

Singleton
"""
from functools import wraps

# 使用__new__方法構造單例類
class Singleton(object):
    def __new__(cls, *args, **kwargs):
        if not hasattr(cls, '_instance'):
            cls._instance = super(Singleton, cls).__new__(cls, *args, **kwargs)
        return cls._instance

print Singleton()
print Singleton()

# 使用單例裝飾器構造單例類
def singleton(cls):
    instances = {}
    @wraps(cls)
    def wrapper(*args, **kwargs):
        if cls not in instances:
            instances[cls] = cls(*args, **kwargs)
        return instances[cls]
    return wrapper

@singleton
class MyClass(object):
    pass

print MyClass()
print MyClass()

# 使用getInstance方法構造單例對象，非線程安全
class MySingleton(object):
    @classmethod
    def getInstance(cls):
        if not hasattr(cls, '_instance'):
            cls._instance = cls()
        return cls._instance

print MySingleton.getInstance()
print MySingleton.getInstance()

輸出結果：

<__main__.Singleton object at 0x00BBFBD0>
<__main__.Singleton object at 0x00BBFBD0>
<__main__.MyClass object at 0x00BBFC30>
<__main__.MyClass object at 0x00BBFC30>
<__main__.MySingleton object at 0x00BBFC90>
<__main__.MySingleton object at 0x00BBFC90>

測試代碼：

import __init__, unittest, threading
from singleton import Singleton, MyClass, MySingleton

class TestSingleton(unittest.TestCase):
    def setUp(self):
        self.singleton_instances = [Singleton() for x in range(100)]
        self.my_class_instances = [MyClass() for x in range(100)]
        self.my_singleton_instances = [MySingleton.getInstance() for x in range(100)]

    def tearDown(self):
        del self.singleton_instances, self.my_class_instances, self.my_singleton_instances

    def test_singleton(self):
        for x in self.singleton_instances:
            self.assertIs(x, Singleton())

    def test_my_class(self):
        for x in self.my_class_instances:
            self.assertIs(x, MyClass())

    def test_my_singleton(self):
        for x in self.my_singleton_instances:
            self.assertIs(x, MySingleton.getInstance())


if __name__ == "__main__":
    unittest.main()