39：类和对象4（拾遗）

一、类的组合

将类的实例化放入新类内，即将旧类组合进新类

类间的纵向关系用继承

类间的横向关系用组合

扩展：Mix-in编程机制

class Turtle:
def __init__(self, x):
self.num = x

class Fish:
def __init__(self, x ):
self.num = x
class Pool:
def __init__(self, x, y):
self.turtle = Turtle(x)
self.fish = Fish(y)

def print_num(self):
print( '水池里总共有乌龟 %d只，小鱼%d条！' % (self.turtle.num, self.fish.num))

>>> pool = Pool(1, 10)
>>> pool.print_num()
水池里总共有乌龟 1只，小鱼10条！

二、类、类对象、实例对象

>>> class C:
count = 0

>>> a = C()
>>> b = C()
>>> c = C()

类定义：C

类对象：C

实例对象：a b c

>>> a.count
0
>>> b.count
0
>>> c.count +=10
>>> c.count
10
>>> C.count += 100
>>> a.count
100
>>> b.count
100
>>> c.count
10

>>> class C:
def x(self):
print('X-man!')

>>> c = C()
>>> c.x()
X-man!
>>> c.x = 1
>>> c.x
1
>>> c.x()
Traceback (most recent call last):
File "<pyshell#8>", line 1, in <module>
c.x()
TypeError: 'int' object is not callable

三、定义类的一些原则

1.少吃多餐：不要试图用一个类定义所有想到的方法和属性，应定义多个类

2.注意词性：类的定义用名词，方法用动词

四、绑定

Python严格要求方法需要有实例才能被调用，这种限制其实就是Python所谓的绑定

>>> class CC:
   def setXY(self, x, y):
       self.x = x
       self.y = y
   def printXY(self):
       print(self.x, self.y)

>>> dd = CC()
>>> dd.__dict__
{}
>>> CC.__dict__
mappingproxy({'__module__': '__main__', 'setXY': <function CC.setXY at 0x03433F18>, 'printXY': <function CC.printXY at 0x03433F60>, '__dict__': <attribute '__dict__' of 'CC' objects>, '__weakref__': <attribute '__weakref__' of 'CC' objects>, '__doc__': None})
>>> dd.setXY(4, 5)
>>> dd.__dict__
{'x': 4, 'y': 5}
>>> del CC
>>> ee = CC()
Traceback (most recent call last):
File "<pyshell#31>", line 1, in <module>
ee = CC()
NameError: name 'CC' is not defined
>>> dd.printXY()
4 5

类实例化后，类删除，类的实例化对象可继续正常工作

39：类和对象4（拾遗）

猜你喜欢