python实现单例模式

#装饰器实现单例模式
def singleton1(func):
    instance={}
    def inner(*args,**kwargs):
        if func not in instance:
           instance[func]=func(*args,**kwargs)
        return instance[func]
    return inner
@singleton1
class user():
    pass
foo1=user()
foo2=user()
print(foo1 is foo2)

#使用修改基类实现单例模式
class Singleton2():
    def __new__(cls, *args, **kwargs):
        if not hasattr(cls, ‘_instance‘):
            cls._instance = super().__new__(cls, *args, **kwargs)
        return cls._instance

class Foo(Singleton2):
    pass


foo3 = Foo()
foo4 = Foo()

print( foo3 is foo4)

#使用类实现单例模式，配合多线程
import threading
import time
class Singleton(object):
    _lock=threading.Lock()
    def __init__(self):
        time.sleep(1)

    @classmethod
    def instance(cls, *args, **kwargs):
        if not hasattr(Singleton, "_instance"):
            with Singleton._lock:
                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()

time.sleep(20)
obj=Singleton.instance()
print(obj)

#使用元类实现单例模式
class SingletonType(type):
    _instance_lock = threading.Lock()
    def __call__(cls, *args, **kwargs):
        if not hasattr(cls, "_instance"):
            with SingletonType._instance_lock:
                if not hasattr(cls, "_instance"):
                    cls._instance = super(SingletonType,cls).__call__(*args, **kwargs)
        return cls._instance

class Foo(metaclass=SingletonType):
    def __init__(self,name):
        self.name = name


obj1 = Foo(‘name‘)
obj2 = Foo(‘name‘)
print(obj1 is obj2)