趣学Python-教孩子学编程--第八章

如何使用类和对象

知识点：

1、函数继承和调用

函数就是对象的动作

继承是指子类中的对象可以使用父类的函数属性，调用需self.函数名（见Go_Eat(self)函数）

class Animals:
    def breathe(self):
        print("breathing")
    def move(self):
        print("moving")
    def eat_food(self):
        print("eating food")
class Mammals(Animals):
    def feed_young_with_milk(self):
        print("feeding young")
class Giraffes(Mammals):
    def eat_leaves_from_trees(self):
        print("eating leaves")
    def Go_Eat(self):
        self.move()
        self.eat_food()
reginald = Giraffes()
reginald.Go_Eat()

moving
eating food

2、初始化对象

当我们创建对象时，有时我们会设置一些值以便将来使用（这些值也称之为“属性”）。例如，当我们想在创建长颈鹿对象时设置一个在它身上斑点的数量，这件事要在初始化时做。

class Giraffes:
    def __init__(self,spots):
        self.giraffe_spots = spots

        #我们把参数spots设置给self函数的一个叫giraffe_spots的对象变量（也就是它的属性）
ozwald = Giraffes(100)
print(ozwald.giraffe_spots)

100

__init__    前后都是两个下划线

课后练习：

1、长颈鹿乱舞

class Giraffes():
    def Left_Foot_Forward(self):
        print("left foot forward")
    def Left_Foot_Backward(self):
        print("left foot back")
    def Right_Foot_Forward(self):
        print("right foot forward")
    def Right_Foot_Backward(self):
        print("right foot back")
    def dance(self):
        self.Left_Foot_Forward()
        self.Left_Foot_Backward()
        self.Right_Foot_Forward()
        self.Right_Foot_Backward()
        self.Left_Foot_Backward()
        self.Right_Foot_Backward()
        self.Right_Foot_Forward()
        self.Left_Foot_Forward()
reginald = Giraffes()
reginald.dance()

left foot forward
left foot back
right foot forward
right foot back
left foot back
right foot back
right foot forward
left foot forward

2、海龟叉子

import turtle
t1 = turtle.Pen()
t2 = turtle.Pen()
t3 = turtle.Pen()
t4 = turtle.Pen()
t1.forward(50)
t1.left(90)
t1.forward(20)
t1.right(90)
t1.forward(20)
t2.forward(40)
t2.left(90)
t2.forward(30)
t2.right(90)
t2.forward(30)
t3.forward(50)
t3.right(90)
t3.forward(20)
t3.left(90)
t3.forward(20)
t4.forward(40)
t4.right(90)
t4.forward(30)
t4.left(90)
t4.forward(30)

之前理解的有误：

       t = turtle.Pen()

       这应该是创建画笔，不是创建画布，一个画布中可以创建多个画笔，如图所示