Python单例模式

本文简单介绍一下如何使用Python实现单例模式

1. 方法一，利用classmethod

import threading

class Test():
    _instance = None
    _instance_lock = threading.Lock()
    def __init__(self):
        pass

    @classmethod
    def get_instance(cls):
    	with cls._instance_lock:
    		if not Test._instance:
    			Test._instance = cls()
    		return Test._instance

a = Test()
print a.get_instance()
a = Test()
print a.get_instance()
a = Test()
print a.get_instance()
a = Test()
print a.get_instance()

执行结果

➜  ~ python test-singlestone.py
<__main__.Test instance at 0x1074dfcf8>
<__main__.Test instance at 0x1074dfcf8>
<__main__.Test instance at 0x1074dfcf8>
<__main__.Test instance at 0x1074dfcf8>

2. 方法二，利用__new__方法

import threading

_PLUGIN_DIRECTORY = None

class Test(object):
	_instance_lock = threading.Lock()
 
 	# 方式一
	# _instance = None
	# def __new__(cls):
	# 	with Test._instance_lock:
	# 		if not Test._instance:
	# 			Test._instance = object.__new__(cls)
	# 		return Test._instance

	def __init__(self):
		pass
	
    # 方式二
 	def __new__(cls):
		with Test._instance_lock:
			if not hasattr(Test, "_instance"):
				Test._instance = object.__new__(cls)
			return Test._instance

a = Test()
b = Test()
print a, b

执行结果

➜  ~ python test-singlestone.py
<__main__.Test object at 0x1075a4d90> <__main__.Test object at 0x1075a4d90>

3. 方法三，全局变量

import threading

_PLUGIN_DIRECTORY = None

class Test():
    _instance = None
    _instance_lock = threading.Lock()
    def __init__(self):
        pass

    @classmethod
    def get_instance(cls):
    	with cls._instance_lock:
    		if not Test._instance:
    			Test._instance = cls()
    		return Test._instance

def create_test_object():
	global _PLUGIN_DIRECTORY
	if not _PLUGIN_DIRECTORY:
		_PLUGIN_DIRECTORY = Test()
	return _PLUGIN_DIRECTORY

a = create_test_object()
b = create_test_object()
print a, b

执行结果：

➜  ~ python test-singlestone.py
<__main__.Test instance at 0x105342368> <__main__.Test instance at 0x105342368>