class Singleton(object):

? ? _instance = None

? ? def __new__(cls, *args, **kwargs):
? ? ? ? if cls._instance is None:
? ? ? ? ? ? cls._instance = object.__new__(cls, *args, **kwargs)
? ? ? ? return cls._instance

if __name__ == '__main__':
? ? instance1 = Singleton()
? ? instance2 = Singleton()
? ? instance3 = Singleton()

? ? # 打印出 3 個(gè)實(shí)例對(duì)象的內(nèi)存地址，判斷是否相同。
? ? print(id(instance1))
? ? print(id(instance2))
? ? print(id(instance3))

def singleton(cls):

? ? _instance = {}

? ? def _singleton(*args, **kargs):
? ? ? ? if cls not in _instance:
? ? ? ? ? ? _instance[cls] = cls(*args, **kargs)
? ? ? ? return _instance[cls]

? ? return _singleton

@singleton
class Singleton(object):
? ? """單例實(shí)例"""

? ? def __init__(self, arg1):
? ? ? ? self.arg1 = arg1

if __name__ == '__main__':
? ? instance1 = Singleton("xag")
? ? instance2 = Singleton("xingag")

? ? print(id(instance1))
? ? print(id(instance2))

class Singleton(object):

? ? _instance = None
? ? _instance_lock = threading.Lock()

? ? def __new__(cls, *args, **kwargs):
? ? ? ? if cls._instance is None:
? ? ? ? ? ? with cls._instance_lock:
? ? ? ? ? ? ? ? cls._instance = object.__new__(cls, *args, **kwargs)
? ? ? ? return cls._instance

def task(arg):
? ? instance = Singleton()
? ? print(id(instance), '\n')

if __name__ == '__main__':
? ? for i in range(3):
? ? ? ? t = threading.Thread(target=task, args=[i, ])
? ? ? ? t.start()