习题39-41.md

class Song(object):
    
    def __init__(self,lyrics):
        self.lyrics = lyrics
        
    def sing_me_a_song(self):
        for line in self.lyrics:
            print(line)
        
happy_baby = Song(["Happy birthday to you",
                   "I don't want to get sued",
                   "SO I'll stop right there"])

bull_on_parade = Song(["They rally around the family",
                       "With pockets full of shells"])

happy_baby.sing_me_a_song()

bull_on_parade.sing_me_a_song()

Happy birthday to you
I don't want to get sued
SO I'll stop right there
They rally around the family
With pockets full of shells

class TheThing(object):
    
    def __init__(self):
        self.number = 0
        
    def some_function(self):
        print("I got called.")
        
    def add_me_up(self,more):
        self.number += more
        return self.number
    
a = TheThing()
b = TheThing()

a.some_function()
b.some_function()

print(a.add_me_up(20))
print(b.add_me_up(30))

print(a.number)
print(b.number)

class TheMultiplier (object):
    
    def __init__(self,base):
        self.base = base
        
    def do_it(self,m):
        return m*self.base

x = TheMultiplier(a.number)
print(x.do_it(b.number))

I got called.
I got called.
20
30
20
30
600