课后练习 第一阶段：Python开发基础 day30 面向对象--单例模式实例

day30 课后作业

1.在元类中控制把自定义类的数据属性都变成大写

class MyMeta(type):
    def __new__(cls,name,bases,attr):
        dic = {}
        for k,v in attr.items():
            if not k.startswith('__'):
                dic[k.upper()] = v
            else:
                dic[k] = v
        return type.__new__(cls,name,bases,dic)

class Demo(metaclass=MyMeta):
    name = 'forever'
    age = 18

print(Demo.__dict__)

2.在元类中控制自定义的类无需init方法

class MyMeta(type):
    def __call__(self, *args, **kwargs):
        obj = object.__new__(self)
        for k,v in kwargs.items():
            obj.__dict__[k] = v
        return obj

class Demo(metaclass=MyMeta):
    name = 'forever'
    age = 18

demo = Demo(name = 'forever',age = 18)
print(demo.__dict__)

3.在元类中控制，把自定义的类的属性都放到attr字典中

class MyMeta(type):
    def __new__(cls,name,bases,attr):
        dic = {'attr':{}}

        for k,v in attr.items():
            if not k.startswith('__'):
                dic['attr'][k] = v
            else:
                dic[k] = v
        return type.__new__(cls,name,bases,dic)

class Demo(metaclass=MyMeta):
    name = 'forever'
    age = 18

print(Demo.__dict__)

4.四种方式实现单例模式

  • 第一种（通过类的绑定方法）

    dic = {'PORT':3306,'HOST':'127.0.0.1'}
class Demo1():
    _instance = None
    def __init__(self,port,host):
        self.port = port
        self.host = host

    @classmethod
    def get_sigoleton(cls):
        if not cls._instance:
            cls._instance = cls(dic['PORT'],dic['HOST'])
        return cls._instance

s1 = Demo1.get_sigoleton()
s2 = Demo1.get_sigoleton()
s3 = Demo1(33306,'192.168.1.1')
print(s1)
print(s2)
print(s3)

  • 第二种(通过装饰器)

    • 用户输入端口和地址，实例化产生对象

    • 当用户不输入端口和地址，每次拿到的对象，都是同一个

    dic = {'PORT':3306,'HOST':'127.0.0.1'}
def get_sigoleton(cls):
    _instance=None
    def wrapper(*args,**kwargs):
        if len(args)!=0 or len(kwargs)!=0:
            #表示传了参数，生成新对象
            res=cls(*args,**kwargs)
            return res
        else:
            nonlocal _instance
            if not _instance:
                _instance=cls(dic['PORT'], dic['HOST'])
            return _instance
    return wrapper

@get_sigoleton    #会把下面的Sql当中参数传入,相当于：Sql=get_sigoleton(Sql)
class Sql():
    def __init__(self,port,host):
        self.port=port
        self.host=host
s1=Sql()
s2=Sql()
s3=Sql('33306','192.168.1.1')
s4=Sql('33306','192.168.1.1')
print(s1)
print(s2)
print(s3)

  • 第三种（通过元类）

    • 当用户输入端口和地址，实例化产生新对象
    • 当用户不输入端口和地址，每次拿到的对象，都是同一个
    dicc = {'PORT':'3306','HOST':'127.0.0.1'}
class Mymeta(type):
    def __init__(self,name,bases,dic):
        #self 是Sql类

        #把实例化好的对象，放到了类的名称空间
        self._instance=self(dicc['PORT'], dicc['HOST'])
    def __call__(self, *args, **kwargs):
        #self是谁？是Sql类
        if len(args)!=0 or len(kwargs)!=0:
            obj=object.__new__(self)
            obj.__init__(*args, **kwargs)
            return obj
        else:
            return self._instance

class Sql(metaclass=Mymeta):    #相当于 Sql=Mymeta(name,bases,dic)   这个会调用 Mymeta的__init__  在里面已经向类的名称空间放了一个对象
    def __init__(self,port,host):
        self.port=port
        self.host=host

print(Sql.__dict__)
s1=Sql()
#调用元类的__call__
s2=Sql()
s3=Sql('33306','192.168.1.1')
print(s1)
print(s2)
print(s3)

  • 第四种（通过模块导入：python中的模块是天然的单例）

    def test():
    from sigonleton import s1
    print(s1.port)
    print(s1)
def test2():
    from sigonleton import s1 as s2
    print(s2)

test()
test2()
from sigonleton import s1
from sigonleton import Sql
s2=Sql(3306,'192.168.1.1')
print(s1)
print(s2)

# 被调用的 sigonleton.py文件
def test():
    from sigonleton import s1
    print(s1.port)
    print(s1)
def test2():
    from sigonleton import s1 as s2
    print(s2)

test()
test2()
from sigonleton import s1
from sigonleton import Sql
s2=Sql(3306,'192.168.1.1')
print(s1)
print(s2)
posted @ 2019-09-04 22:38  foreversun92  阅读(192)  评论(0)  编辑  收藏  举报