Python实现单例常用的几种方式

雨点打透心脏的1/2处 2022-02-20 11:27 221阅读 0赞

### 1.最简单的，日常都在用 ###

**import 模式，Python天然的单例模式**

# mysingleton.py 中定义
    class My_singleton(object):
    	a = 1111
    	def foo(self):
    		pass
    my_singleton = My_singleton()
    
    # 在另一个py文件中导入对象my_singleton
    from mysingleton import my_singleton
    
    print(my_singleton.a)
    >>>>
    1111

--------------------

### 2.装饰器版本 ###

def singleton(cls,*args,**kwargs):
    	instance = { }
    	def getinstance():
    		if cls not in instance:
    			instance[cls] = cls(*args,**kwargs)
    		return instance[cls]
    	return getinstance
    
    @singleton
    class Myclass(object):
    	pass

--------------------

### 3.共享属性 ###

**创建时把所有实例的\_\_dict\_\_指向同一个字典，这样它们具有相同的属性和方法**

class Borg(object):
    	_state = { }
    	def __new__(cls,*args,**kwargs):
    		ob = supper(Borg,cls).__new__(cls,*args,**kwargs)
    		ob.__dict__ = cls._state
    		return ob
    
    class Myclass(Borg):
    	pass

--------------------

### 4.使用\_\_new\_\_ ###

*  **无线程安全锁**

class Singleton(object):
    	def __new__(cls,*args,**kwargs):
    		if not hasattr(cls,'_instance'):
    			orig = super(Singleton,cls)
    			cls._instance = orig.__new__(cls,*args,**kwargs)
    		return cls._instance

--------------------

*  **有线程安全锁**

import threading
    class Singleton(object):
    	_instance_lock = threading.Lock()
    	def __init__(self):
    		pass
    	def __new__(cls,*args,**kwargs):
    		if not hasattr(Singleton,'_instance'):
    			with Singleton._instance_lock:
    				if not hasattr(Singleton,'_instance'):
    					Singleton._instance = object.__new__(cls)
    		return Singleton._instance