中心思想 ： 在例項之前判斷 該類的屬性有沒有被例項化過。 如果沒有就例項話， 有的話就返回上一次例項話

第一種： 通過 python 自帶的 __new__ 去實現

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

obj1 = Singleton()
obj2 = Singleton()
print(obj1,obj2)

第二種： 通過裝飾器

def Sing(cls):
    _instance = {}
    def _sig(*args, **kwargs):
        if cls not in _instance:
            _instance[cls] 
 
= cls(*args, **kwargs)
        return _instance[cls]
    return _sig



@Sing
class A:
    def __init__(self):
        self.x = 1


a1 = A()
a2 = A()
print(a1, a2)

轉載部落格：https://www.cnblogs.com/huchong/p/8244279.html