《python无师自通》第十四章 深入面向对象编程

视代码如诗词，勿要做无所谓的堆砌

class Rectangle():
    recs = []#类变量


    def __init__(self,w,l):
        self.width = w#实例变量
        self.length = l
        self.recs.append((self.width,
                          self.length))


    def print_size(self):
        print("""{} by {}""".
              format(self.width,
                     self.length))

r1 = Rectangle(10,24)
r2 = Rectangle(20,40)
r3 = Rectangle(100,200)

print(Rectangle.recs)

[(10, 24), (20, 40), (100, 200)]

魔法方法

使用魔法方法前

class Lion:
    def __init__(self,name):
        self.name = name

lion = Lion("Dilbert")
print(lion)
    

使用魔法方法后

class Lion:
    def __init__(self,name):
        self.name = name


    def __repr__(self):#继承的魔法方法
        return self.name

lion = Lion("Dilbert")
print(lion)
    

class AlwaysPositive:
    def __init__(self,number):
        self.n = number


    def __add__(self,other):#魔法方法
        return abs(self.n +
                   other.n)
    

x = AlwaysPositive(20)
y = AlwaysPositive(-30)
print(x + y)

is

class Person:
    def __init__(self):
        self.name = "Bob"
      


bob = Person()
same_bob = bob
print(bob is same_bob)#指向相同的对象

another_bob = Person()
print(bob is another_bob)#指向不同的对象

x = 10
if x is None:
    print("x is None :(")
else:
    print("x is not None")

x = None
if x is None:
    print("x is None")

if x is not None:
    print("x is None:(")

挑战练习

1．向 Square 类中添加一个 square_list 类变量，要求每次新创建一个 Square
对象时，新对象会被自动添加到列表中。

class Square():
    resc = []
    
    def __init__(self,att):
        self.attend = att       
        self.resc.append(att)

r1 = Square(10)
r2 = Square(1)

print(Square.resc)

2．修改 Square 类，要求在打印 Square 对象时，打印的信息为图形 4 个边的长
度。例如，假设创建一个 Square(29)，则应打印 29 by 29 by 29 by 29。

class Square():
    resc = []
    
    def __init__(self,att):
        self.attend = att       
        self.resc.append(att)
        print("{} by {} by {} by {}".format(att,att,att,att))

r = Square(29)

3．编写一个函数，接受两个对象作为参数，如果为相同的对象则返回 True，反之
返回 False。

x = input("请输入x：")
y = input("请输入y：")

if x == y:
    print(x is y)
else:
    print(x is y)