类的继承
基本概念
定义
格式如下
继承中的访问控制
class Animal:__CNOUT = 0HEIGHT = 0def __init__(self,age,weight,height):self.__CNOUT =self.__CNOUT + 1self.age = ageself.__weight = weightself.HEIGHT = heightdef eat(self):print('{} eat'.format(self.__class__.__name__))def __getweight(self):print(self.__weight)@classmethoddef showcount1(cls):print(cls.__CNOUT)@classmethoddef __showcount2(cls):print(cls.__CNOUT)class Cat(Animal):NAME = 'CAT'c = Cat(3,5,15) c.eat() c.showcount1()#注意此处的cls.__COUNT仍为0print(c.NAME) print(c.__dict__)#{'_Animal__CNOUT': 1, 'age': 3, '_Animal__weight': 5, 'HEIGHT': 15} print(Cat.__dict__)#{'__module__': '__main__', 'NAME': 'CAT', '__doc__': None} print(Animal.__dict__)#{'__module__': '__main__', '_Animal__CNOUT': 0, 'HEIGHT': 0,...}
方法的重写、覆盖override
class Animal:def shout(self):print('Animal shout')class Cat(Animal):#覆盖父类的方法def shout(self):print('miao')#覆盖自身的方法，显示调用了父类的方法def shout(self):print(super(Cat, self))super().shout()a = Animal() a.shout() c =Cat() c.shout()#输出结果： # Animal shout # <super: <class 'Cat'>, <Cat object>> # Animal shout
class Animal:@classmethoddef class_method(cls):print('class_method_animal')@staticmethoddef static_method():print('static_method_animal')class Cat(Animal):@classmethoddef class_method(cls):print('class_method_cat')@staticmethoddef static_method():print('static_method_cat')c = Cat() c.class_method() c.static_method() #输出结果： # class_method_cat # static_method_cat
继承中的初始化
示例1
class A:def __init__(self):self.a1 = 'a1'self.__a2 = 's2'print('A init')class B(A):pass b = B() print(b.__dict__) #{'a1': 'a1', '_A__a2': 's2'}
示例2
class A:def __init__(self):self.a1 = 'a1'self.__a2 = 's2'print('A init')class B(A):def __init__(self):self.b1 = 'b1'print('B init') b = B() print(b.__dict__) #{'b1': 'b1'}
class A:def __init__(self):self.a1 = 'a1'self.__a2 = 's2'print('A init')class B(A):def __init__(self):# A.__init__(self)# super(B,self).__init__()super().__init__()self.b1 = 'b1'print('B init') b = B() print(b.__dict__) #{'a1': 'a1', '_A__a2': 's2', 'b1': 'b1'}
如何正确初始化
class Animal:def __init__(self,age):print('Animal init')self.age =agedef show(self):print(self.age)class Cat(Animal):def __init__(self,age,weight):super().__init__(age)#c.show()结果为11print('Cat init')self.age = age + 1self.weight = weight# super().__init__(age)#c.show()结果为10 c = Cat(10,5) c.show()
# c.__dict__ {'age': 11, 'weight': 5}
class Animal:def __init__(self,age):print('Animal init')self.__age =agedef show(self):print(self.__age)class Cat(Animal):def __init__(self,age,weight):super().__init__(age)print('Cat init')self.__age = age + 1self.__weight = weight c = Cat(10,5) c.show() print(c.__dict__)#{'_Animal__age': 10, '_Cat__age': 11, '_Cat__weight': 5}
Python不同版本的类
多继承
多继承弊端
Python多继承实现
class ClassName(基类列表):类体
多继承的缺点
Mixin
class Printable:def _print(self):print(self.content)class Document:#假设为第三方库，不允许修改def __init__(self,content):self.content = contentclass Word(Document):pass#假设为第三方库，不允许修改 class Pdf(Document):pass#假设为第三方库，不允许修改class PrintableWord(Printable,Word):pass print(PrintableWord.__dict__) print(PrintableWord.mro()) pw = PrintableWord('test string') pw._print()
def printable(cls):def _print(self):print(self.content,'装饰器')cls.print = _printreturn clsclass Document:#假设为第三方库，不允许修改def __init__(self,content):self.content = contentclass Word(Document):pass#假设为第三方库，不允许修改 class Pdf(Document):pass#假设为第三方库，不允许修改 @printable class PrintableWord(Word):passprint(PrintableWord.__dict__)#{'__module__': '__main__', '__doc__': None, 'print': <function printable.<locals>._print at 0x0000000002961730>} PrintableWord('test').print()#test 装饰器
4.Mixin
#Mixin示例1 class PrintableMixin:def print(self):print(self.content,'Mixin')class Document:def __init__(self,content):self.content = contentclass Word(Document):pass class Pdf(Document):passclass PrintableWord(PrintableMixin,Word):pass print(PrintableWord.__dict__) print(PrintableWord.mro())pw = PrintableWord('test\nstring') pw.print()
#Mixin示例2 class PrintableMixin:def print(self):print(self.content,'Mixin')class Document:def __init__(self,content):self.content = contentclass Word(Document):pass class Pdf(Document):passclass SuperPrintableMixin(PrintableMixin):def print(self):print('~'*20)super().print() #通过继承复用print('~'*20)class SuperPrintablePdf(SuperPrintableMixin,Pdf):pass print(SuperPrintablePdf.__dict__) print(SuperPrintablePdf.mro())spp = SuperPrintablePdf('super print pdf') spp.print()
Mixin类
练习
#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 import mathclass Shape:@propertydef area(self):raise NotImplementedError('基类未实现')class Triangle(Shape):def __init__(self,a,b,c):self.a = aself.b = bself.c = c@propertydef area(self):p = (self.a+self.b+self.c)/2return math.sqrt(p*(p-self.a)*(p-self.b)*(p-self.c))class Circle(Shape):def __init__(self,radius):self.radius = radius@propertydef area(self):return math.pi*self.radius**2class Rectangle(Shape):def __init__(self,width,height):self.width = widthself.height = height@propertydef area(self):return self.width*self.height# shapes = [Triangle(3,4,5),Rectangle(3,4),Circle(4)] # for s in shapes: # print('The area of {} = {}'.format(s.__class__.__name__,s.area))#2.圆类的数据可序列化 import json import msgpackdef mydump(cls):def _dumps(self, t='json'):if t == 'json':return json.dumps(self.__dict__)elif t == 'msgpack':return msgpack.packb(self.__dict__)else:raise NotImplementedError('没有实现的序列化')cls.dumps = _dumpsreturn cls#使用Mixin类 # class SerializableMixin: # def dumps(self,t='json'): # if t == 'json': # return json.dumps(self.__dict__) # elif t == 'msgpack': # return msgpack.packb(self.__dict__) # else: # raise NotImplementedError('没有实现的序列化') # #使用装饰器 @mydump class SerializableCircleMixin(Circle):passscm = SerializableCircleMixin(1) print(scm.area)#3.141592653589793 print(scm.__dict__)#{'radius': 1} print(scm.dumps('json'))#{"radius": 1}
作业
#单链表 class SingleNode:#代表一个节点def __init__(self,val,next=None):self.val = valself.next = Noneclass LinkedList:#容器类，某种方式存储一个个节点def __init__(self):self.head = Noneself.tail = Nonedef append(self,val):node = SingleNode(val)if self.head is None:# 0self.head = nodeself.tail = nodeself.tail.next = nodeself.tail = nodedef iternodes(self):while self.head:yield self.head.valself.head = self.head.next
1 #实现双向链表 2 class SingleNode: 3 #代表一个节点 4 def __init__(self,val,next=None,prev=None): 5 self.val = val 6 self.next = next 7 self.prev = prev 8 9 def __repr__(self): 10 return str(self.val) 11 12 class LinkedList: 13 #容器类，某种方式存储一个个节点 14 def __init__(self): 15 self.head = None 16 self.tail = None 17 18 def append(self,val): 19 node = SingleNode(val) 20 if self.head is None:# 0 21 self.head = node 22 else: 23 self.tail.next = node 24 node.prev = self.tail 25 self.tail = node 26 27 def pop(self): 28 if self.tail is None:#0 29 raise NotImplementedError('Empty') 30 tail = self.tail 31 prev= self.tail.prev 32 if prev is None:#1个节点 33 self.head = None 34 self.tail = None 35 else:#>1 36 self.tail = prev 37 prev.next = None 38 return tail.val 39 40 41 def insert(self,index,val):#1,7 42 if index < 0: 43 raise Exception('Error') 44 cur = None 45 for i,current in enumerate(self.iternodes()): 46 if i == index: 47 cur = current 48 break 49 50 if cur is None:#说明索引越界或空链表，直接末尾追加 51 self.append(val) 52 return 53 54 node = SingleNode(val) 55 prev = cur.prev 56 if prev is None:#1个节点,头部插入 57 self.head = node 58 node.next = cur 59 cur.prev = node 60 else:#>=2 61 node.next = cur 62 prev.next = node 63 cur.prev = node 64 node.prev = prev 65 66 def iternodes(self,reversed = False): 67 current = self.head 68 while current: 69 yield current 70 current = current.next 71 72 a = SingleNode(1) 73 b = SingleNode(2) 74 c = SingleNode(3) 75 d = SingleNode(4) 76 e = SingleNode(5) 77 f = SingleNode(6) 78 ll = LinkedList() 79 ll.append(a) 80 ll.append(b) 81 ll.append(c) 82 ll.append(d) 83 ll.append(e) 84 ll.append(f) 85 # ll.insert(1,0) 86 # ll.insert(0,0) 87 ll.insert(10,100) 88 print('pop元素：',ll.pop()) 89 print('pop元素：',ll.pop()) 90 print('pop元素：',ll.pop()) 91 ll.insert(0,10) 92 93 for node in ll.iternodes(): 94 print(node)
