python 单例模式

单例模式

多次实例化的结果指向同一个实例

单例模式实现方式

方式一:

import settings

class MySQL:
    __instance = None

    def __init__(self, ip, port):
        self.ip = ip
        self.port = port

    @classmethod
    def from_conf(cls):
        if cls.__instance is None:
            cls.__instance = cls(settings.IP,settings.PORT)
        return cls.__instance

obj1 = MySQL.from_conf()
obj2 = MySQL.from_conf()
obj3 = MySQL.from_conf()
print(obj1)
print(obj2)
print(obj3)

方式二:

import settings

def singleton(cls):
    _instance = cls(settings.IP, settings.PORT)

    def wrapper(*args, **kwargs):
        if args or kwargs:
            obj = cls(*args, **kwargs)
            return obj
        return _instance

    return wrapper

@singleton
class MySQL:
    def __init__(self, ip, port):
        self.ip = ip
        self.port = port

obj1 = MySQL()
obj2 = MySQL()
obj3 = MySQL()
print(obj1)
print(obj2)
print(obj3)

方式三:

import settings

class Mymeta(type):
    def __init__(self, class_name, class_bases, class_dic):
        self.__instance = self(settings.IP, settings.PORT)

    def __call__(self, *args, **kwargs):
        if args or kwargs:
            obj = self.__new__(self)
            self.__init__(obj, *args, **kwargs)
            return obj
        else:
            return self.__instance

class MySQL(metaclass=Mymeta):
    def __init__(self, ip, port):
        self.ip = ip
        self.port = port

obj1 = MySQL()
obj2 = MySQL()
obj3 = MySQL()
print(obj1)
print(obj2)
print(obj3)

方式四:

def f1():
    from singleton import instance
    print(instance)

def f2():
    from singleton import instance,MySQL
    print(instance)
    obj = MySQL('1.1.1.1', '3389')
    print(obj)

f1()
f2()


singleton.py文件里内容:
import settings

class MySQL:
    print('run...')

    def __init__(self, ip, port):
        self.ip = ip
        self.port = port

instance = MySQL(settings.IP, settings.PORT)