單例的實現方式:
1、基於類
#encoding=utf-8
class Singleton(object):
def __init__(self):
pass
@classmethod
def instance(cls, *args, **kwargs):
if not hasattr(Singleton, "_instance"):
Singleton._instance = Singleton(*args, **kwargs)
return Singleton._instance
s1 = Singleton.instance()
s2 = Singleton.instance()
print(s1 is s2)
支持多線程:
#encoding=utf-8
import threading
class Singleton(object):
_instance_lock = threading.Lock()
def __init__(self):
pass
@classmethod
def instance(cls, *args, **kwargs):
if not hasattr(Singleton, "_instance"):#
with Singleton._instance_lock:#枷鎖
if not hasattr(Singleton, "_instance"):
Singleton._instance = Singleton(*args, **kwargs)
return Singleton._instance
def task(arg):
obj = Singleton.instance()
print(obj)
for i in range(10):
t = threading.Thread(target=task,args=(i,))
t.start()
obj = Singleton.instance()
print(obj)
2、利用__new__()
#encoding=utf-8
class Singleton(object):
def __init__(self):
pass
def __new__(cls,*args,**kwargs):
if not hasattr(cls,"_instance"):
cls._instance = object.__new__(cls)
return cls._instance
p1 = Singleton()
p2 = Singleton()
print(p1 is p2)
支持多線程方式
#encoding=utf-8
import threading
class Singleton(object):
_instance_lock = threading.Lock()
def __init__(self):
pass
def __new__(cls,*args,**kwargs):
if not hasattr(cls,"_instance"):
with cls._instance_lock:
if not hasattr(cls,"_instance"):
cls._instance = object.__new__(cls)
return cls._instance
def task():
obj = Singleton()
print(obj)
for i in range(20):
t = threading.Thread(target=task,args=())
t.start()
3、利用裝飾器
#encoding=utf-8
import threading
def Singleton(cls):
_instance = {}
def _singleton(*args,**kwargs):
if cls not in _instance:
_instance[cls] = cls(*args,**kwargs)
return _instance[cls]
return _singleton
@Singleton
class Person(object):#Person = Singleton(Person)
a = 10
def __init__(self,x=0):
self.x = x
p = Person(2)#_singleton(2)
p2 = Person(3)
print(p is p2)
print(p.x)
print(p2.x)
示例1：
#encoding=utf-8
class Person(object):
__instance = None#定義一個類變量，用於綁定實例對象
def __init__(self,name,age):
self.name = name
self.age = age
@classmethod
def get_instance(cls,name,age):
if cls.__instance == None:
cls.__instance =Person(name,age)
return cls.__instance
def get_info(self):
return self.name + ":" + str(self.age)
p1 = Person.get_instance("xxx",20)
p2 = Person.get_instance("yyy",50)
print(p1 is p2)
print(p1.get_info())
print(p2.get_info())
#此種實現方式無法在生成實例後改變實例變量的值
示例2：
#encoding=utf-8
class Singleton(object):
_instance = None
def __new__(cls,a,b,*args,**kwargs):
if cls._instance == None:
cls._instance = super(Singleton,cls).__new__(cls,*args,**kwargs)
return cls._instance
class Person(Singleton):
def __init__(self,name,age):
self.name = name
self.age = age
def getInfo(self):
return "姓名: %s,年齡: %s" %(self.name,self.age)
p1 = Person("張三",20)
print(p1.getInfo())
p2 = Person("李四",20)
print(p1.getInfo())
print(p1 is p2)
print("類變量: ",Person._instance)
示例3：
#encoding=utf-8
class Person(object):
__instance = None#創建一個類變量用戶存儲類的實例對象
def __init__(self,name,age):
self.name = name
self.age = age
def __new__(cls,name,age):#自定義Person自己的__new__()方法用於產生實例對象，此處需要傳入name，age兩個參數
if cls.__instance == None:#保證實例對象__instance只會被賦值一次，如果之前已經創建過實例，直接返回之前創建的實例
#cls.__instance = super(Person,cls).__new__(cls)
cls.__instance = object.__new__(cls)#調用父類的__new__方法創建對象
return cls.__instance#返回實例對象
def getInfo(self):
return "姓名: %s,年齡: %s" %(self.name,self.age)
p1 = Person("h",20)
print(p1.getInfo())
p2 = Person("kkk",30)
print(p1.getInfo())
print(p2.getInfo())
print(p1 is p2)
'''
以上代碼執行過程：
p1 = Person("h",20)
首先調用__new__方法產生實例p1，此時Person的__instance爲none所以會創建一個對象，
然後調用__init__方法，把返回的實例對象__instance傳入self中，並初始實例變量name，age
print(p2.getInfo())
首先調用__new__方法產生實例p2，此時Person的__instance爲不爲None,爲p1,所以會直接返回對象p1，
然後調用__init__方法，把返回的實例對象__instance傳入self中，並用新的name，age初始實例變量name，age
'''
如果__init__有其他參數，__new__需要傳入參數
單例的實現方式
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