2019.9.4学习整理

2019.9.4学习整理

单例模式

什么是单例模式

单例模式：基于某种某种方法实例化多次得到实例是同一个

为什么用单例模式

当实例化多次得到的对象中存放的属性都一样的情况，应该将多个对象指向同一个内存，即同一个实例

单例模式的四种方法

1.单例模式（类的绑定方法）

#settings.py
PORT=3306
HOST='127.0.0.1'



class Mysql:
    _instacane=None

    def __init__(self,PORT,HOST):
        self.PORT=PORT
        self.HOST=HOST
    @classmethod
    def get_sigoleton(cls):
        import settings
        if cls._instacane:
            return cls._instacane
        else:
            cls._instacane=cls(settings.PORT,settings.HOST)
        return cls._instacane

s1=Mysql.get_sigoleton()
s2=Mysql.get_sigoleton()
s3=Mysql(3306,'172.0.0.1')
print(s1)
print(s2)
print(s3)

2.通过装饰器

#settings.py
PORT=3306
HOST='127.0.0.1'


def get_sigoleton(cls):
    import settings
    _instance=cls(settings.PORT,settings.HOST)
    def wrapper(*args,**kwargs):
        if len(args)!=0 or len(kwargs)!=0:
            res=cls(*args,**kwargs)
            return res
        else:
            return _instance
    return wrapper

@get_sigoleton
class Mysql():
    def __init__(self,PORT,HOST):
        self.PORT=PORT
        self.HOST=HOST

s1=Mysql()
s2=Mysql()
s3=Mysql('3306','192.168.1.1')
s4=Mysql('3306','192.168.1.1')
print(s1)
print(s2)
print(s3)
print(s4)

3.通过元类

#settings.py
PORT=3306
HOST='127.0.0.1'


class Mymate(type):
    def __init__(self,name,bases,dic):
        import settings
        self._instance=self(settings.PORT,settings.HOST)
    def __call__(self, *args, **kwargs):
        if len(args)!=0 or len(kwargs)!=0:
            obj=object.__new__(self)
            obj.__init__(*args,**kwargs)
            return obj
        else:
            return self._instance


class Mysql(metaclass=Mymate):
    def __init__(self,PORT,HOST):
        self.PORT=PORT
        self.HOST=HOST

s1=Mysql()
s2=Mysql()
s3=Mysql(3306,'127.0.1.1')
print(s1)
print(s2)
print(s3)

4.使用模块

#settings.py
PORT=3306
HOST='127.0.0.1'


#sigoleton.py
import settings
class Mysql():
    def __init__(self, PORT, HOST):
        self.PORT = PORT
        self.HOST = HOST

s1 = Mysql(settings.PORT, settings.HOST)




def test():
    from  sigoleton import s1
    print(s1)
def test1():
    from  sigoleton import s1 as s2
    print(s2)

test()
test1()

from sigoleton import s1
from sigoleton import Mysql
s2=Mysql(3306,'192.168.1.1')
print(s1)
print(s2)