python：类与基类简介(一)

一：继承：基类和派生类

区分“属于”（is-a）和“具有”（has-a）这两种关系。“属于”即为继承：在这种关系中，派生类的一个对象也属于“基类”的一个对象。

“具有”即为“合成”：这种关系中，一个对象“具有”对其他类的一个或多个对象的引用，后者是前者的成员。

基类即超类，派生类即子类

创建派生类的格式：

class Paishenclassname(Jileiclassname):
    ...

#class  派生类名（基类名）：
    ....
#即：表示Paishenclass  类   继承了  Jileiclass的所有属性、方法

下面的例子，

补充知识：

issubclass(A,B),判断A类是否是B类的子类；

isinstance(a,A）,判断a是否是A类的对象；

A.__bases__,返回A类的基类，如果没有基类，返回<class'object'>

举例：关于圆是点的子类；

import math
class Point:
    '''Class that represents geometric point'''
    def __init__(self,xValue=0,yValue=0):
        '''Point constructor take x and y coordinates'''
        self.x=xValue
        self.y=yValue
class Circle(Point):
    '''Class that represents a circle'''
    def __init__(self,x=0,y=0,radiusValue=0.0):
        '''Circle corstructor takes x and y coordinates of center
        point and radius'''
        Point.__init__(self,x,y)#class base-class constructor
        self.radius=float(radiusValue)
    def area(self):
        '''Computes area of a Circle'''
        return math.pi * self.radius ** 2
#main program
#examine classes Point and Circle
print("Point bases:",Point.__bases__)
print("Circle bases:",Circle.__bases__)

print("Point is a subclass of Circle:",issubclass(Point,Circle))
print("Circle is a subclass of Point:",issubclass(Circle,Point))

point =Point(30,50)#create Point object
circle=Circle(120,89,2.7)#create Circle object
print("\ncircle is a Circle object:",isinstance(circle,Point))
print("point is a Circle object:",isinstance(point,Circle))
print("Circle is a point object:",isinstance(circle,Point))

#print Point and Circle objects
print ("\npoint members:\n\t",point.__dict__)
print("circle menbers:\n\t",circle.__dict__)


print("\nArea of circle:",circle.area())

运行结果：

Point bases: (<class 'object'>,)
Circle bases: (<class '__main__.Point'>,)
Point is a subclass of Circle: False
Circle is a subclass of Point: True

circle is a Circle object: True
point is a Circle object: False
Circle is a point object: True

point members:
	 {'x': 30, 'y': 50}
circle menbers:
	 {'x': 120, 'y': 89, 'radius': 2.7}

Area of circle: 22.902210444669596

python：类与基类简介(一)

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