28面向对象3_继承_linkedlist

 

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目录

inheritance继承:...1

继承中的访问控制:...5

继承中的初始化:...9

多继承:...13

mixin:...16

习题:...23

single linkedlist.25

double linkedlist:...28

习题:...32

 

 

 

inheritance继承:

人类和猪类都继承自动物类;

个体继承自父母,继承了父母的一部分特征,但也可以有自己的个性;

在面向对象的世界中,从父类继承,就可直接拥有父类的属性和方法,这样可减少代码、多复用;

子类可定义自己的属性和方法;

 

子类继承父类的特征,特征即类属性、类方法、静态方法、实例属性;

公共的属性和方法,包括_开头的;

隐私属性和方法是__开头的,对外暴露提供的方法要为属性装饰器的方法;

 

open-close-principle开闭原则:

对扩展开放(继承开放),扩展个性化的地方;

修改关闭;

 

继承也称派生;

class Cat(Animal)这种形式就是从父类继承,括号中写继承的类的列表;

继承可让子类从父类获取特征(属性和方法);

父类,Animal就是Cat的父类,也称基类、超类;

子类,Cat就是Animal的子类,也称派生类;

 

定义:

class 子类(基类1[,基类2,...]):

         语句块

如果定义类时,没有基类列表,等同于继承自object,在python3中,object是所有对象的根基类,倒置的根;

python2中有古典类(旧式类)、新式类,3.0全是新式类;

python支持多继承,继承也可以多级,多级展开即tree,不一定是二叉树;

单继承(一条链串起来);多继承;

 

单继承关系图:

子类指向父类;

28面向对象3_继承_linkedlist

 

继承的特殊属性和方法:

__base__,类的基类,过时了;

__bases__,类的基类元组;

__mro__,多继承时用,显示方法查找顺序,基类的元组,多继承中非常重要,mro()方法的结果会放在__mro__里;

mro(),多继承时用,同上,int.mro(),在类上用该方法,实例上不能用;

__subclasses__(),类的子类列表,int.__subclasses__();

 

python不同版本的类:

py2.2之前,类是没有共同的祖先的,之后,引入object类,它是所有类的共同祖先类object;

py2为了兼容,分为古典类(旧式类)和新式类;

py3中全是新式类;

新式类都是继承自object类的,新式类可使用super();

py2与py3版本不同,不仅是语法方面,还有类构建方面;

 

例:

class Animal(object):   #等价于class Animal:,默认继承自object,若加上object则兼容python2

    x = 123

    def __init__(self):

        self.name = 'tom'

 

    def getname(self):

        return self.name

 

class Cat(Animal):

    pass

 

class Dog():

    pass

 

tom = Cat()

print(tom.name)

print(tom.__dict__)

print(tom.getname())

 

dog = Dog()

# print(dog.name)

# print(dog.getname())

输出:

tom

{'name': 'tom'}

tom

 

例:

class Animal(object):

    x = 123

    def __init__(self,name):

        self._name = name

 

    @property   #装饰后的也能继承,终归Animal类的管辖

    def name(self):

        return self._name   #公共属性

 

    def shout(self):

        print('Animal shout')

 

class Cat(Animal):

    x = 'cat'   #override覆盖

    def shout(self):   #override覆盖(重写),与rewrite是两码事

        print('miao')

 

class Dog(Animal):

    pass

 

class Garfield(Cat):

    pass

 

class PersiaCat(Cat):

    # def __init__(self):   #call to __init__ of super class is missed,需调用父类方法

    #     self.eyes = 'blue'

    pass

 

tom = Cat('tom')

print(tom.name)

print(tom.__dict__)

tom.shout()   #自有的,体现个性

 

dog = Dog('ahuang')

dog.shout()   #自己没有的,用继承的'Animal shout'

 

gf = Garfield(Cat)

gf.shout()

 

pc = PersiaCat('persiacat')

print(pc.__dict__)

# pc.name = 'persiacat'   #不可修改

pc.eyes = 'blue,green'

pc.shout()

print(pc.name,pc.eyes)

print(pc.__dict__)

输出:

tom

{'_name': 'tom'}

miao

Animal shout

miao

{'_name': 'persiacat'}

miao

persiacat blue,green

{'_name': 'persiacat', 'eyes': 'blue,green'}

 

例:

gf = Garfield(Cat)

gf.shout()

print('gf.mro={}'.format(gf.__class__.mro()))   #mro()方法,只能在类上用,不能在实例上用

print('gf.mro={}'.format(gf.__class__.__mro__))

print('gf.bases={}'.format(gf.__class__.__bases__))

输出:

miao

gf.mro=[, , , ]

gf.mro=(, , , )

gf.bases=(,)

 

例:

In [1]: int.__subclasses__()

Out[1]: [bool, sre_constants._NamedIntConstant, ]

In [2]: int.__bases__

Out[2]: (object,)

In [3]: int.__base__

Out[3]: object

In [4]: int.mro()   #返回int自身

Out[4]: [int, object]

In [5]: int.__mro__

Out[5]: (int, object)

 

 

 

继承中的访问控制:

从父类继承,自己没有的,就可到父类中找;

私有的都是不可访问的,本质上是改了名并放入所在类的__dict__中,知道这个新名称就可直接找到这个隐藏的变量,这是个黑魔法技巧,慎用;

 

继承时,公有的(除__开头的),子类和实例都可随意访问;私有的,被隐藏,子类和实例不可直接访问,私有变量所在的类内有方法,则可访问这个私有变量;

python通过自己一套实现,实现和其它语言一样的面向对象的继承机制;

 

属性查找顺序:

实例的__dict__-->类__dict__,有继承-->父类__dict__;

如果搜索这些地方后没找到就抛异常,先找到就立即返回了;

 

方法的重写(覆盖)override:

super(),新式类中提供了该方法,可访问到父类的属性,具体原理后续;

Animal.__init__(self,name),py2写法;

super().__init__(name),相当于super(Cat,self).__init__(name)完整写法,py3写法,

self.__class__.__base__.__init__(self,name),不推荐使用;

 

例:

class Animal(object):

    x = 123

    def __init__(self,name):

        self._name = name

        self.__age = 10

 

class Cat(Animal):

    x = 'cat'

 

class Garfield(Cat):

    pass

 

tom = Garfield('tom')

print(tom.__dict__)   #输出隐私属性_Animal__age,_父类的名字__属性,谁有这个属性编译器就改名字为谁,当前只Animal类上有

print(Garfield.__dict__)   #子类先找自己的实例,再依次往上找父类

print(Cat.__dict__)   #类中找不到_Animal__age,该属性在实例里,self即为实例,实例属性的__dict__,方法是在类中

输出:

{'_name': 'tom', '_Animal__age': 10}

{'__module__': '__main__', '__doc__': None}

{'__module__': '__main__', 'x': 'cat', '__doc__': None}

 

例(方法的重写(覆盖)):

class Animal(object):

    x = 123

    def __init__(self,name):

        self._name = name

        self.__age = 10

 

    @property

    def name(self):

        return self._name

 

    def shout(self):

        print('Animal shout')

 

class Cat(Animal):

    x = 'cat'

    def __init__(self,name):

        # super(Cat,self).__init__(name)

        # super().__init__(name)

        Animal.__init__(self,name)   #子类中也初始化,python2写法;py3写法为super().__init__(name),新式类推荐使用此种写法;两种方式等价;

        #self._name = name   #2个属性{'_name': 'tom', '_Animal__age': 10}

                   #self.catname = name   #3个属性{'_name': 'tom', '_Animal__age': 10, 'catname': 'tom'}

                   self._name = 'cat' + name   #2个属性{'_name': 'cattom', '_Animal__age': 10}

 

tom = Cat('tom')

print(tom.name)

print(tom.__dict__)

输出:

#tom

#{'_name': 'tom', '_Animal__age': 10}

#tom

#{'_name': 'tom', '_Animal__age': 10, 'catname': 'tom'}

cattom

{'_name': 'cattom', '_Animal__age': 10}

 

例(方法的重写(覆盖)):

class Animal:

    def shout(self):

        print('Animal shout')

 

class Cat(Animal):

    def shout(self):

        print('miao')

 

    def shout(self):   #覆盖了自身的shout,之前的彻底没有了;Animal中的shout仍在自己内部,在调用时遮盖了;这两次覆盖有差异

        print('cat shout')

        print(super())

        print(super(Cat,self))   #等价于super()

        super().shout()

        self.__class__.__base__.shout(self)   #不推荐使用,等价于super()

 

cat = Cat()

cat.shout()

输出:

cat shout

, >

, >

Animal shout

Animal shout

 

例:

class Animal(object):

    x = 123

    def __init__(self,name):

        self._name = name

        self.__age = 10

 

    @property

    def name(self):

        return self._name

 

    def shout(self):

        print('Animal shout')

 

class Cat(Animal):

    x = 'cat'

    def __init__(self,name):

        # self._name = name

        self._name = 'cat' + name  #先后有影响

        Animal.__init__(self, name)

 

tom = Cat('tom')

print(tom.name)

print(tom.__dict__)

输出:

tom

{'_name': 'tom', '_Animal__age': 10}

 

例:

class Animal:

    @classmethod

    def clsmtd(cls):

        print(cls,cls.__name__)

 

class Cat(Animal):

    def __init__(self,name):

        self.name = name

    @classmethod

    def clsmtd(cls):

        print(cls,cls.__name__)

 

class Garfield(Cat): pass

 

tom = Garfield('tom')

tom.clsmtd()   #多态,多态前提要继承,用哪个类创建的实例就是哪个类

 

print(tom.__dict__)

print(Cat.__dict__)

print(Animal.__dict__)   #公有的(除__开头),父类的都是你的,py内部会自动逐级找(可理解为继承的就是我的),传什么就打印什么,用哪个类创建的实例就是哪个类,虽有父类的特征在都继承下来

输出:

Garfield

{'name': 'tom'}

{'__module__': '__main__', '__init__': , 'clsmtd': , '__doc__': None}

{'__module__': '__main__', 'clsmtd': , '__dict__': , '__weakref__': , '__doc__': None}

 

 

 

继承中的初始化:

好习惯 ,在子类中只要有初始化__init__方法,就要把父类的写上,如super().__init__(name),即如果父类中定义了__init__方法,子类中也有__init__,就该在子类的__init__中调用它;

 

建议:少在继承中使用私有变量;

 

例:

class A:

    def __init__(self,a):

        self.a = a

 

class B(A):   #类B定义时声明继承自类A,则在类B中__bases__中可看到类A,但这和是否调用类A的构造方法是两回事

    def __init__(self,b,c):   #如果B中调用了A的构造方法super().__init__(a)就可拥有父类的属性了,查看b的__dict__

        self.b = b

        self.c = c

 

    def printv(self):

        print(self.b)

        print(self.c)

        # print(self.a)   #AttributeError: 'B' object has no attribute 'a'

 

b = B(20,30)

b.printv()

print(B.__bases__)

 

print(B.__dict__)

print(A.__dict__)

输出:

20

30

(,)

{'__module__': '__main__', '__init__': , 'printv': , '__doc__': None}

{'__module__': '__main__', '__init__': , '__dict__': , '__weakref__': , '__doc__': None}

 

解决上例问题:

class A:

    def __init__(self,a):

        self.a = a

 

class B(A):

    def __init__(self,b,c):

        super().__init__(b+c)   #等价于A.__init__(self,b+c)

        self.b = b

        self.c = c

 

    def printv(self):

        print(self.b)

        print(self.c)

        print(self.a)

 

b = B(20,30)

b.printv()

print(B.__bases__)

 

print(b.__dict__)

print(B.__dict__)

print(A.__dict__)

输出:

20

30

50

(,)

{'a': 50, 'b': 20, 'c': 30}

{'__module__': '__main__', '__init__': , 'printv': , '__doc__': None}

{'__module__': '__main__', '__init__': , '__dict__': , '__weakref__': , '__doc__': None}

 

例:

class A:

    def __init__(self,a,d):

        self.a = a

        self.__d = d

 

class B(A):

    def __init__(self,b,c):

        super().__init__(b+c,c-b)

        self.b = b

        self.c = c

        self.__d = b + c + 1

 

    def printv(self):

        print(self.b)

        print(self.c)

        print(self.a)

        print(self.__d)

 

b = B(20,30)

b.printv()

print(b.__class__.__bases__)

 

print(b.__dict__)

print(B.__dict__)

print(A.__dict__)

输出:

20

30

50

51

(,)

{'a': 50, '_A__d': 10, 'b': 20, 'c': 30, '_B__d': 51}   #实例b的__dict__中有的私有属性,要查看该私有属性必须在该实例所在类中有方法,如果该实例的类中没有访问方法,父类中有同样属性的访问方法,那最终访问的是父类中的属性

{'__module__': '__main__', '__init__': , 'printv': , '__doc__': None}

{'__module__': '__main__', '__init__': , '__dict__': , '__weakref__': , '__doc__': None}

 

例:

class Animal:

    def __init__(self,age):

        print('Animal init')

        self.__age = age

 

    def show(self):

        print(self.__age)

 

class Cat(Animal):

    def __init__(self,age,height):

        print('Cat init')

        super().__init__(age)

        self.__age = age + 1

        self.__height = height

 

c = Cat(10,20)

c.show()   #show方法在Animal中定义,__age会被解释为_Animal__age,这样设计不好,Cat的实例应显示自己的属性值

print(c.__dict__)

print(Cat.__dict__)

print(Animal.__dict__)

输出:

Cat init

Animal init

10

{'_Animal__age': 10, '_Cat__age': 11, '_Cat__height': 20}

{'__module__': '__main__', '__init__': , '__doc__': None}

{'__module__': '__main__', '__init__': , 'show': , '__dict__': , '__weakref__': , '__doc__': None}

 

解决上例问题:

一个原则,自己的私有属性,就该自己的方法读取和修改,不要借助其它类的方法,即使是父类或派生类的方法;

class Animal:

    def __init__(self,age):

        print('Animal init')

        self.__age = age

 

    def show(self):

        print(self.__age)

 

class Cat(Animal):

    def __init__(self,age,height):

        print('Cat init')

        super().__init__(age)

        self.__age = age + 1

        self.__height = height

 

    def show(self):

        print(self.__age)

        print(self.__height)

 

c = Cat(10,20)

c.show()

print(c.__dict__)

print(Cat.__dict__)

print(Animal.__dict__)

输出:

Cat init

Animal init

11

20

{'_Animal__age': 10, '_Cat__age': 11, '_Cat__height': 20}

{'__module__': '__main__', '__init__': , 'show': , '__doc__': None}

{'__module__': '__main__', '__init__': , 'show': , '__dict__': , '__weakref__': , '__doc__': None}

 

 

 

多继承:

ocp原则,open-closed principle,多继承、少修改;

继承的用途:增强基类、实现多态;

 

多态:

在面向对象中,父类、子类通过继承联系在一起,如果可通过一套方法,就可实现不同表现,就是多态;

一个类继承自多个类,就是多继承,它将具有多个类的特征;

 

多继承弊端:

多继承很好的模拟了世界,因为事物很少是单一继承,但是舍弃简单,必然引入复杂性,带来了冲突;

如同一个孩子继承了来自父母双方的特征,那么到底眼睛像爸爸还是妈妈呢?孩子更像谁多一点?

多继承的实现会导致编译器设计的复杂度增加,所以现在很多语言也舍弃了类的多继承,C++支持多继承,java舍弃了多继承;

 

java中,一个类可实现多个接口,一个接口也可继承多个接口,java的接口很纯粹,只是方法的声明,继承者必须实现这些方法,就具有了这些能力,就能干什么;

 

多继承可能会带来二异性,如猫和狗都继承自动物类,如果一个类多继承了猫类和狗类,猫和狗都有shout方法,子类空间继承谁的shout呢?

解决方案:

实现多继承的语言,可解决二义性,深度优先或广度优先;

 28面向对象3_继承_linkedlist

注:单一继承;

 

28面向对象3_继承_linkedlist

多继承,分开看两条均单继承:

MyClass-->D-->B-->A,深度优先;

MyClass-->D-->C-->B-->A,广度优先;

 

多继承带来路径选择问题,究竟继承哪个父类的特征呢?

py使用MRO,method resolution order,解决基类搜索顺序问题;

历史原因,MRO有三个搜索算法:

经典算法,按定义从左到右,深度优先策略,2.2之前,MyClass->D->B->A->C->A;

新式类算法,经典算法的升级,重复的只保留一个,2.2,MyClass->D->B->C->A->object;

C3算法,在类被创建出来时,就计算出一个MRO有序列表,2.3之后,py3唯一支持的算法,MyClass->D->B->C->A->object;

 

多继承的缺点:

当类很多,继承复杂的情况下,继承路径太多,很难说清什么样的继承路径;

py语法允许多继承,但py代码是解释执行,只有执行到的时候才发现错误;

团队协作开发,如果引入多继承,那代码将不可控;

不管编程语言是否支持多继承,都应避免多继承;

py的面向对象,太灵活了,太开放了,所以要团队守规矩,类增加要规范;

规范化、文档化、大量重构;

 

多继承定义:

class ClassName(基类列表):

         类体

 

 

 

mixin:

UML中,面向对象中的高级部分;

 

例:

28面向对象3_继承_linkedlist

Document类是其它所有文档类的抽象基类;

Word、Pdf是Document类的子类;

要求:

为document子类提供打印能力;

 

思路1:

在Document类中提供print方法;

基类提供的方法不应该具体实现,因为它未必适合子类的打印,子类中需要覆盖重写;

print算是一种能力——打印功能,不是所有的Document的子类都需要的,所以,从这个角度出发,有问题;

 

思路2:

需要打印的子类上增加;

如果在子类上直接增加,违反了ocp原则,所以应该继承后增加;

28面向对象3_继承_linkedlist

以下两种不同的继承思路,不同场景下用:

方一:用于项目正在开发中,直接加到所属类里;

方二:用于已开发完成项目或第三方库,用继承方式新增类;

看似不错,如果还要提供其它能力,如何继承?

应用于网络,文档应该具备序列化的能力,类上就应该实现序列化;

可序列化还可能分为使用pickle、messagepack、json等;

这时发现,类可能太多了,继承的方式不是很好了,功能太多,A类需要某几样功能,B类需要另几样功能,很繁琐;

 

思路3:

装饰器,用处极广;

优点:简单方便,在需要的地方动态增加;

用装饰器增强一个类,把功能给类附加上去,哪个类需要,就装饰它;

 

思路4:

mixin,本质上就是多继承实现的;

mixin体现的是一种组合的设计模式;

在面向对象的设计中,一个复杂的类,往往需要很多功能,而这些功能由来自不同的类提供,这就要将很多的类组合在一起;

从设计模式的角度来说,多组合(混在一起,如PrintableWord(PrintableMixin,Word))、少继承,组合优于继承;

28面向对象3_继承_linkedlist

 

mixin类的使用原则:

mixin类中不应该显式的出现__init__初始化方法(是混进去增强功能的,不用初始化,一般是用来增强类属性,而不是增强实例的,实例缺的东西应在其类上或继承的类上,而不是混进去的);

mixin类通常不能独立工作(不完整),因为它是准备混入别的类中的部分功能实现;

mixin类如有继承,该mixin类的祖先类也应是mixin类;

 

使用时,mixin类通常在继承列表的第一个位置,如class SuperPrintablePdf(SuperPrintableMixin,Pdf): pass;

 

mixin类和装饰器:

这两种方式都可使用,看个人喜好;

如果还需要继承,就要使用mixin类方式;

简单用装饰器;复杂用mixin类;

实现方式不同,结果一样(殊途同归);

 

 

思路2:方一:

class Document:

    def __init__(self,content):

        self.content = content

 

    def print(self):

        print(self.content)

 

class Word(Document):   #用于项目正在开发中,直接加到所属类里

    def print(self):

        print('word print: {}'.format(self.content))

 

class Pdf(Document):

    def print(self):

        print('pdf print: {}'.format(self.content))

 

print(Word.mro())

word = Word('test\nabc')

word.print()

print(Word.__dict__)

输出:

[, , ]

word print: test

abc

{'__module__': '__main__', 'print': , '__doc__': None}

 

思路2:方二1:

class Document:   #第三方库

    def __init__(self,content):

        self.content = content

 

    def print(self):

        print(self.content)

 

class Word(Document): pass   #第三方库

 

class PrintableWord(Word):

    def print(self):

        print('word print: {}'.format(self.content))

 

class Pdf(Document): pass   #第三方库

 

class PrintablePdf(Pdf):

    def print(self):

        print('pdf print: {}'.format(self.content))

 

print(PrintableWord.mro())

word = PrintableWord('test\nabc')

word.print()

print(word.__dict__)

print(PrintableWord.__dict__)

输出:

[, , , ]

word print: test

abc

{'content': 'test\nabc'}

{'__module__': '__main__', 'print': , '__doc__': None}

 

思路2:方二2:

class Printable:

    def _print(self):

        print(self.content)

 

class Document:

    def __init__(self,content):

        self.content = content

 

    def print(self):

        print(self.content)

 

class Word(Document): pass

 

class PrintableWord(Printable,Word): pass

 

class Pdf(Document): pass

 

class PrintablePdf(Printable,Pdf): pass

 

print(PrintableWord.mro())

word = PrintableWord('test\nabc')

word.print()

print(word.__dict__)

print(PrintableWord.__dict__)

输出:

[, , , , ]

test

abc

{'content': 'test\nabc'}

{'__module__': '__main__', '__doc__': None}

 

思路3(函数装饰器):

def printable(cls):

    # def _print(self):

    #     print(self.content)

    # cls.print = _print   #等价于下面一行

    cls.print = lambda self: print(self.content)

    return cls

 

class Document:

    def __init__(self,content):

        self.content = content

 

    def print(self):

        print(self.content)

 

class Word(Document): pass

 

class Pdf(Document): pass

 

@printable

class PrintableWord(Word): pass

 

@printable

class PrintablePdf(Pdf): pass

 

word = PrintableWord('test\nabc')

word.print()

print(word.__class__.mro())

print(word.__dict__)

print(PrintableWord.__dict__)

输出:

test

abc

[, , , ]

{'content': 'test\nabc'}

{'__module__': '__main__', '__doc__': None, 'print': . at 0x7f32371490d0>}

 

思路4:

class PrintableMixin:

    def print(self):  #该行和下一行的print,与builtins中冲突?不冲突,这是自定义类中的方法;若把该函数写在与class同级下,就与builtins冲突了

        print('~~~~~~~~~~~~~~~~')

        print(self.content)

        print('~~~~~~~~~~~~~~~~')

 

class Document:

    def __init__(self,content):

        self.content = content

 

class Word(Document): pass

 

class PrintableWord(PrintableMixin,Word): pass  #PrintableMixin只能在前边,如在右边将不起作用,属多继承,本质上是改变了__mro__中的顺序

 

class Pdf(Document): pass

 

class PrintablePdf(PrintableMixin,Pdf): pass

 

class SuperPrintableMixin(PrintableMixin):   #mixin是类,可继承

    def print(self):

        print('#####################')

        print(self.content)

        print('#####################')

 

class SuperPrintablePdf(SuperPrintableMixin,Pdf): pass

 

word = PrintableWord('test\nabc')

word.print()

print(word.__class__.mro())   #查看搜索顺序

print(word.__dict__)

print(word.__class__.__dict__)

 

pdf = SuperPrintablePdf('pdf\npdf')

pdf.print()

print(pdf.__class__.mro())

print(pdf.__dict__)

print(pdf.__class__.__dict__)

输出:

~~~~~~~~~~~~~~~~

test

abc

~~~~~~~~~~~~~~~~

[, , , , ]

{'content': 'test\nabc'}

{'__module__': '__main__', '__doc__': None}

#####################

pdf

pdf

#####################

[, , , , , ]

{'content': 'pdf\npdf'}

{'__module__': '__main__', '__doc__': None}

 

 

 

习题:

1、shape基类,要求所有子类都必须提供面积的计算,子类有三角形、矩形、圆;

2、上题圆类的数据可序列化;

3、用面向对象实现linked list链表:

单向链表实现append、iternodes;

双向链表实现append、pop、insert、remove、iternodes;

 

28面向对象3_继承_linkedlist

 

注:

pycharm中格式化,Code-->Reformat Code;

文档字符串一般用""",双引号三引号;

 

1、

import math

 

class Shape:

    @property

    def area(self):

        # return

        raise NotImplementedError('base class is not implement')  #技巧,基类中未实现该方法,即这个父类就是不允许调用

 

class Triangle(Shape):

    def __init__(self,bottom,height):

        self.bottom = bottom

        self.height = height

 

    @property

    def area(self):

        return self.bottom * self.height / 2

 

class Rectangle(Shape):

    def __init__(self,length,width):

        self.length = length

        self.width = width

 

    @property

    def area(self):

        return self.length * self.width

 

class Circle(Shape):

    def __init__(self,radius):

        self.radius = radius

 

    @property

    def area(self):

        return math.pi * (self.radius ** 2)

 

triangle = Triangle(3,2)

print(triangle.area)

 

rectangle = Rectangle(5,4)

print(rectangle.area)

 

circle = Circle(2)

print(circle.area)

输出:

3.0

20

12.566370614359172

 

2、

import json

import msgpack

from class_practice_8 import Circle

 

class SerializableMixin:

    def dumps(self,t='json'):

        if t == 'json':

            return json.dumps(self.__dict__)

        elif t == 'msgpack':

            return msgpack.dumps(self.__dict__)

        else:

            raise NotImplementedError('Not implemented serializable')

 

class SerializableCircleMixin(SerializableMixin,Circle): pass

 

scm = SerializableCircleMixin(2)

print(scm.area)

 

print(scm.__dict__)

s = scm.dumps('msgpack')

print(s)

输出:

12.566370614359172

{'radius': 2}

b'\x81\xa6radius\x02'

 

single linkedlist

链表与列表?链表为什么用列表实现?

列表中仅保存的是链表中每个元素内存地址的引用;

链表中每个元素之间是靠自身内部的next联系的;

 

单向链表,手拉手,有序,内存中是乱的、分散的;

list,内存中有序;

 

3、

single linkedlist1:

class SingleNode:

    def __init__(self,val,next=None):

        self.val = val

        self.next = next

 

    def __repr__(self):

        return str(self.val)

 

    def __str__(self):

        return str(self.val)

 

class LinkedList:

    def __init__(self):

        # self.nodes = []

        self.head = None

        self.tail = None

 

    def append(self,val):

        node = SingleNode(val)

        if self.tail is None:

            self.head = node

        else:

            self.tail.next = node

        # self.nodes.append(node)

        self.tail = node

 

    def iternodes(self):

        current = self.head

        while current:

            yield current

            current = current.next

 

ll = LinkedList()

node = SingleNode(5)

ll.append(node)

node = SingleNode(6)

ll.append(node)

for node in ll.iternodes():

    print(node)

输出:

5

6

 

single linkedlist2:

class SingleNode:   #代表一个节点

    def __init__(self,val,next=None):   #最后一个为None

        self.val = val

        self.next = next   #实例属性,类中print和装饰器中的_print

 

    def __repr__(self):

        return str(self.val)

 

    __str__ = __repr__

 

class LinkedList:   #容器类,某种方式存储一个个节点

    def __init__(self):

        self.items = []   #保存每个节点的地址;可用索引,便于查询,检索方便,但insert、remove不方便,[]适合读多写少;业务中如果频繁插入元素则不用列表

        self.head = None

        self.tail = None  #追加方便

 

    def append(self,val):

        node = SingleNode(val)

        if self.tail is None:   #尾巴是空则该链表为空

            self.head = node

        else:

            self.tail.next = node

        self.tail = node

        self.items.append(node)

       

    def iternodes(self):   #要知道链表中的元素必须迭代;技巧:generator

        current = self.head

        while current:

            yield current

            current = current.next

 

    def __getitem__(self, item):  #仅用于容器,提供一种方便的接口,如索引或其它方式来用

        return self.items[item]

 

         def __len__(self):   #很少拿长度,频繁操作长度一直在变,只是大概

        return len(self.items)

 

ll = LinkedList()

node = SingleNode(5)

ll.append(node)

node = SingleNode(6)

ll.append(node)

for node in ll.iternodes():

    print(node)

 

print(ll[0])

输出:

5

6

5

2

 

 

 

double linkedlist:

 

技巧:

generator;

三目运算符;

enumerate();

 

class SingleNode:

    def __init__(self,val,next=None,prev=None):

        self.val = val

        self.next = next

        self.prev = prev

 

    def __repr__(self):

        return str(self.val)

 

    __str__ = __repr__

 

class LinkedList:

    def __init__(self):

        # self.items = []

        self.head = None

        self.tail = None

 

    def append(self,val):

        node = SingleNode(val)

        if self.tail is None:   #第一个node,the first node

            self.head = node

        else:

            self.tail.next = node

            node.prev = self.tail   #当前节点的上一个节点

        self.tail = node

        # self.items.append(node)

 

    def iternodes(self,reverse=False):

        current = self.tail if reverse else self.head  #2个技巧,generator函数和类三目运算符

        while current:

            yield current

            current = current.prev if reverse else current.next

 

    def pop(self):

        if self.tail is None:   #链表中元素为0

            raise Exception('Empty')

        tail = self.tail

        prev = tail.prev

        # next = tail.next   #用不上,尾巴的下一个元素一定为None

        if prev is None:   #尾巴的前一个元素为空,说明该链表仅一个元素

            self.head = None

            self.tail = None   #把当前尾巴的元素清空后,链表就为空

        else:   #链表中元素>1个

            self.tail = prev

            prev.next = None

        return tail.val

 

    def getitem(self,index):

        if index < 0:

            return None

        current = None

        for i,node in enumerate(self.iternodes()):   #技巧

            if i == index:

                current = node

                break

        if current is None:   #如下四行可简写为if current is not None: return current

            return None

        else:

            return current

 

    def insert(self,index,val):   #考虑当前链表,0个元素,1个元素(index为0、1时),尾部追加

        if index < 0:

            raise Exception('Error')

        current = None

        for i,node in enumerate(self.iternodes()):

            if i == index:

                current = node

                break

        if current is None:   #链表中无元素,index只要大于边界就往里追加

            self.append(val)

            return

        prev = current.prev

        # next = current.next

        node = SingleNode(val)

        if prev is None:   #前加、中间加、尾部加

            self.head = node

            node.next = current

            current.prev = node

        else:

            node.prev = prev

            node.next = current

            current.prev = node

            prev.next = node

 

    def remove(self,index):

        if self.tail is None:

            raise Exception('Empty')

        if index < 0:

            raise ValueError('Wrong Index{}'.format(index))

        current = None

        for i,node in enumerate(self.iternodes()):

            if i == index:

                current = node

                break

        if current is None:

            raise ValueError('Wrong Index {} out of memory'.format(index))

        prev = current.prev

        next = current.next

        if prev is None and next is None:

            self.head = None

            self.tail = None

        elif prev is None:

            self.head = next

            next.prev = None

        elif next is None:

            self.tail = prev

            prev.next = None

        else:

            prev.next = next

            next.prev = prev

        del current

 

 

ll = LinkedList()

node1 = SingleNode('abc')

ll.append(node1)

node2 = SingleNode(4)

ll.append(node2)

node3 = SingleNode(5)

ll.append(node3)

node4 = SingleNode(6)

ll.append(node4)

node5 = SingleNode('end')

ll.append(node5)

 

for node in ll.iternodes():

    print(node)

print('~'*20)

ll.pop()

ll.pop()

ll.pop()

ll.insert(0,'start')   #各种测试,前、中、尾,元素为空,元素为1个

ll.insert(8,'end')

ll.insert(1,123)

ll.insert(2,456)

ll.remove(5)

ll.remove(0)

for node in ll.iternodes(reverse=True):

    print(node)

输出:

abc

4

5

6

end

~~~~~~~~~~~~~~~~~~~~

4

abc

456

123

 

 

 

习题:

1、将链表,封装成容器:

要求:

1)提供__getitem__()、__iter__()、__setitem__();

2)使用一个列表,辅助完成上面的方法;

3)进阶:不使用列表,完成上面的方法;

 

2、实现类property装饰器,类名称为Property;

 

1、方一(容器实现):

 

class SingleNode:

    def __init__(self,val,next=None,prev=None):

        self.val = val

        self.next = next

        self.prev = prev

 

    def __repr__(self):

        return str(self.val)

 

    __str__ = __repr__

 

class LinkedList:

    def __init__(self):

        self.items = []

        self.head = None

        self.tail = None

        self.size = 0

 

    def append(self,val):

        node = SingleNode(val)

        if self.tail is None:

            self.head = node

        else:

            self.tail.next = node

            node.prev = self.tail

        self.tail = node

        self.items.append(node)

        self.size += 1

 

    def iternodes(self,reverse=False):

        current = self.tail if reverse else self.head

        while current:

            yield current

            current = current.prev if reverse else current.next

 

    def pop(self):

        if self.tail is None:

            raise Exception('Empty')

        tail = self.tail

        prev = tail.prev

        # next = tail.next

        if prev is None:

            self.head = None

            self.tail = None

        else:

            self.tail = prev

            prev.next = None

        self.items.pop()

        self.size -= 1

        return tail.val

 

    def getitem(self,index):

        if index < 0:

            return None

        current = None

        for i,node in enumerate(self.iternodes()):

            if i == index:

                current = node

                break

        if current is None:

            return None

        else:

            return current

 

    def insert(self,index,val):

        if index < 0:

            raise Exception('Error')

        current = None

        for i,node in enumerate(self.iternodes()):

            if i == index:

                current = node

                break

        if current is None:

            self.append(val)

            return

        prev = current.prev

        # next = current.next

        node = SingleNode(val)

        if prev is None:

            self.head = node

            node.next = current

            current.prev = node

        else:

            node.prev = prev

            node.next = current

            current.prev = node

            prev.next = node

        self.items.insert(index,val)

        self.size += 1

 

    def remove(self,index):

        if self.tail is None:

            raise Exception('Empty')

        if index < 0:

            raise ValueError('Wrong Index{}'.format(index))

        current = None

        for i,node in enumerate(self.iternodes()):

            if i == index:

                current = node

                break

        if current is None:

            raise ValueError('Wrong Index {} out of memory'.format(index))

        prev = current.prev

        next = current.next

        if prev is None and next is None:

            self.head = None

            self.tail = None

        elif prev is None:

            self.head = next

            next.prev = None

        elif next is None:

            self.tail = prev

            prev.next = None

        else:

            prev.next = next

            next.prev = prev

        del current

        self.items.pop(index)

        self.size -= 1

 

    def __len__(self):

        return self.size

 

    # def __iter__(self):

    #     return iter(self.items)

    __iter__ = iternodes

 

    def __getitem__(self, item):

        return self.items[item]

 

    def __setitem__(self, key, value):

        self.items[key].val = value   #如果出错,借用列表来抛异常,不需自己实现

 

ll = LinkedList()

node1 = SingleNode('abc')

ll.append(node1)

node2 = SingleNode(4)

ll.append(node2)

node3 = SingleNode(5)

ll.append(node3)

node4 = SingleNode(6)

ll.append(node4)

# ll.remove(3)

node5 = SingleNode('end')

ll.append(node5)

 

for node in ll.iternodes():

    print(node)

print('~'*20)

ll.pop()

node6 = SingleNode('head')

ll.insert(0,node6)

node7 = SingleNode('middle')

ll.insert(3,node7)

ll.remove(3)

# print(len(ll))

for node in ll:

    print(node)

# print(node7.next)   #None

 

 

1、方二(非容器实现):

 

class SingleNode:

    def __init__(self,val,next=None,prev=None):

        self.val = val

        self.next = next

        self.prev = prev

 

    def __repr__(self):

        return str(self.val)

 

    __str__ = __repr__

 

class LinkedList:

    def __init__(self):

        # self.items = []

        self.head = None

        self.tail = None

        self.size = 0

 

    def append(self,val):

        node = SingleNode(val)

        if self.tail is None:

            self.head = node

        else:

            self.tail.next = node

            node.prev = self.tail

        self.tail = node

        # self.items.append(node)

        self.size += 1

 

    def iternodes(self,reverse=False):

        current = self.tail if reverse else self.head

        while current:

            yield current

            current = current.prev if reverse else current.next

 

    def pop(self):

        if self.tail is None:

            raise Exception('Empty')

        tail = self.tail

        prev = tail.prev

        # next = tail.next

        if prev is None:

            self.head = None

            self.tail = None

        else:

            self.tail = prev

            prev.next = None

        # self.items.pop()

        self.size -= 1

        return tail.val

 

    def getitem(self,index):

        if index < 0:

            return None

        current = None

        for i,node in enumerate(self.iternodes()):

            if i == index:

                current = node

                break

        if current is None:

            return None

        else:

            return current

 

    def insert(self,index,val):

        if index < 0:

            raise Exception('Error')

        current = None

        for i,node in enumerate(self.iternodes()):

            if i == index:

                current = node

                break

        if current is None:

            self.append(val)

            return

        prev = current.prev

        # next = current.next

        node = SingleNode(val)

        if prev is None:

            self.head = node

            node.next = current

            current.prev = node

        else:

            node.prev = prev

            node.next = current

            current.prev = node

            prev.next = node

        # self.items.insert(index,val)

        self.size += 1

 

    def remove(self,index):

        if self.tail is None:

            raise Exception('Empty')

        if index < 0:

            raise ValueError('Wrong Index{}'.format(index))

        current = None

        for i,node in enumerate(self.iternodes()):

            if i == index:

                current = node

                break

        if current is None:

            raise ValueError('Wrong Index {} out of memory'.format(index))

        prev = current.prev

        next = current.next

        if prev is None and next is None:

            self.head = None

            self.tail = None


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