2021-10-15 python从入门到精通--第十章 类

类

定义类

class ClassName:
	'''类的帮助信息'''
	statement

创建类实例

ClassName(parameterlist)

创建__init__()方法

class Geese:
	'''大雁类'''
	def __init__(self, beak, wing, claw):
		print("我是大雁类")
		print(beak)
		print(wing)
		print(claw)
		
wildGoose = Geese(beak1, wing1, claw1)

创建类成员并访问

创建实例方法并访问

def functionaName(self, parameterlist):
	block

instanceName.functionName(parametervalue)

创建数据成员并访问

类属性：
在所有实例间共享

>>> class Geese:
...     '''雁类'''
...     neck = "abcd"
...     wing = "efgh"
...     number = 0
...     def __init__(self):
...             Geese.number += 1
...             print(Geese.number)
...
>>> list1 = []
>>> for i in range(4):
...     list1.append(Geese())
...
1
2
3
4
>>> print(Geese.number)
4
>>>	
动态添加类属性：
>>> Geese.beak = "ijkl"
>>> print(list1[1].beak)
ijkl
>>>

实例属性：
只作用于当前实例

>>> class Geese:
...     '''雁类'''
...     def __init__(self):
...             self.neck = "abcd"
...             self.wing = "efgh"
...             print(self.neck)
...             print(self.wing)
...
>>> geese1 = Geese()
abcd
efgh
>>>
动态修改实例属性
>>> geese1.neck = "ijkl"
>>> geese1.neck
'ijkl'
>>>

访问限制

保证某些属性或方法不被外部访问
foo：首尾双下划线，定义特殊方法一般是系统定义名字
__foo：表示private成员，只允许定义该方法的类本身进行访问

>>> class Swan:
...     '''天鹅'''
...     __neck_swan = "abcd"
...     def __init__(self):
...             print(Swan.__neck_swan)
...
>>> swan1 = Swan()
abcd
>>> print(swan1._Swan__neck_swan)		#通过实例名._类名__XXX的方式访问
abcd
>>> print(swan1.__neck_swan)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
AttributeError: 'Swan' object has no attribute '__neck_swan'
>>>

属性

与类属性和实例属性不同

创建用于计算的属性

通过@property(装饰器)将方法转换为属性，可以直接通过方法名访问，而无须再添加小括号

@property
def methodname(self)
	block 

例：

>>> class Rect:
...     def __init__(self, width, height):
...             self.width = width
...             self.height = height
...     @property
...     def area(self):
...             return self.width*self.height
...
>>> rect1 = Rect(800 , 600)
>>> rect1.area
480000
>>>

为属性添加安全保护机制

想要创建一个可以被读取，但是不能被修改的属性，使用@property

>>> class TVshow:
...     def __init__(self, show):
...             self.__show = show
...     @property
...     def show(self):
...             return self.__show
...
>>> tvshow = TVshow("abcdefg")
>>> print(tvshow.show)
abcdefg
>>>

继承

基本语法

class ClassName(baseclasslist):
	'''类的帮助信息'''
	statement

例：

>>> class Fruit:
...     color = "green"
...     def harvest(self, color):
...             print(color)
...
>>> class Apple(Fruit):
...     color = "red"
...     def __init__(self):
...             print("I am apple")
...
>>> apple1 = Apple()
I am apple
>>> apple1.harvest(apple1.color)
red
>>>

方法重写

可以在派生类中重写harvest()方法

>>> class Apple(Fruit):
...     color = "red"
...     def __init__(self):
...             print("I am apple")
...     def harvest(self, color):
...             print("I do not like " + color)
...
>>> apple2 = Apple()
I am apple
>>> apple2.harvest(apple2.color)
I do not like red

派生类中调用基类__init__()方法

如果想要再派生类中调用基类的__init__()方法进行初始化，需要再派生类中使用super()函数

super().__init__()

例:

>>> class Fruit:
...     def __init__(self, color = "green"):
...             Fruit.color = color
...     def harvest(self, color):
...             print(self.color)
...
>>> class Apple(Fruit):
...     color = "red"
...     def __init__(self):
...             print("I am apple")
...             super().__init__()
...
>>> apple3 = Apple()
I am apple
>>> apple3.harvest(apple3.color)
red
>>>