实现单例模式的三种方式

1.使用类的绑定方法实现单例模式

class MySQL():
	__instance = None
	def __init__(self, ip, port):
		self.info = (ip, port)
	@classmethod
	def singleton(cls):
		if cls.__instance is None:
			cls.__instance = object.__new__(cls)
			cls.__instance.__init__('200', 9090)
			return cls.__instance
		else:
			return cls.__instance
obj1 = MySQL.singleton()
obj2 = MySQL.singleton()
print(obj2 is obj1)  # True
obj3 = MySQL(224, 454)
print(obj1, obj2, obj3)

2.使用自定义元类实现单例模式

class Mymeta(type):
	__instance = None
	def __init__(self, class_name, class_bases, class_dic):
		self.__instance = object.__new__(self)
		self.__init__(self.__instance, '127', 9080)
	def __call__(self, *args, **kwargs):
		if args or kwargs:
			obj = object.__new__(self)
			obj.__init__(*args, **kwargs)
			return obj
		else:
			return self.__instance
class MySQL(object, metaclass=Mymeta):

	def __init__(self, ip, port):
		self.info = (ip, port)
obj1 = MySQL()
obj2 = MySQL()
print(obj2 is obj1)
obj3 = MySQL(224, 454)
print(obj1, obj2, obj3)

3.使用装饰器实现单例模式

def wrapper(func):
	_instance = func('127', 8990)
	def inner(*args, **kwargs):
		if args or kwargs:
			return func(*args, **kwargs)
		else:
			return _instance
	return inner
@wrapper
class MySQL(object):

	def __init__(self, ip, port):
		self.info = (ip, port)
obj1 = MySQL()
obj2 = MySQL()
print(obj2 is obj1)
obj3 = MySQL(224, 454)
print(obj1, obj2, obj3)