| 特殊屬性 | 含義 | 示例 |
| __base__ | 類的基類 |
|
| __bases__ | 類的基類元組 | |
| __mro__ | 顯示方法查找順序，基類的元組 | |
| mro() | 同上 | int.mro() |
| __subclasses__() | 類的子類列表 | int.__subclasses__() |
class Animal:
__COUNT = 100
HEIGHT = 0
def __init__(self,age,weight,height):
self.__COUNT += 1
self.age = age
self.__weight = weight
self.HEIGHT = height
def eat(self):
print("{} eat".format(self.__class__.__name__))
def __getweight(self):
print(self.__weight)
@classmethod
def showcount1(cls):
print(cls.__COUNT)
@classmethod
def __showcount2(cls):
print(cls.__COUNT)
def showcount3(self):
print(self.__COUNT)
class Cat(Animal):
NAME = "CAT"
__COUNT = 200
#a = Cat() # TypeError: __init__() missing 3 required positional arguments: 'age', 'weight', and 'height'
a = Cat(30,50,15)
a.eat() # Cat eat
print(a.HEIGHT) # 15
#print(a.__COUNT) # AttributeError: 'Cat' object has no attribute '__COUNT'
#print(a.__showcount2) # AttributeError: 'Cat' object has no attribute '__showcount2'
#print(a.__getweight) # AttributeError: 'Cat' object has no attribute '__getweight'
a.showcount3() # 101
a.showcount1() # 100
print(a.NAME) # CAT
print(Animal.__dict__) # {'__module__': '__main__', '_Animal__COUNT': 100, 'HEIGHT': 0, '__init__': function Animal.__init__ at 0x020DC228>, 'eat': function Animal.eat at 0x020DC468>, '_Animal__getweight': function Animal.__getweight at 0x02126150>, 'showcount1': classmethod object at 0x020E1BD0>, '_Animal__showcount2': classmethod object at 0x020E1890>, 'showcount3': function Animal.showcount3 at 0x021264F8>, '__dict__': attribute '__dict__' of 'Animal' objects>, '__weakref__': attribute '__weakref__' of 'Animal' objects>, '__doc__': None}
print(Cat.__dict__) # {'__module__': '__main__', 'NAME': 'CAT', '_Cat__COUNT': 200, '__doc__': None}
print(a.__dict__) # {'_Animal__COUNT': 101, 'age': 30, '_Animal__weight': 50, 'HEIGHT': 15}
從父類繼承、自己沒有的，就可以到父類中找
私有的都是不可訪問的，但是本質上依然是改了名稱放在這個屬性所在的類的了【__dict__】中，知道這個新民成就可以了直接找到這個隱藏的變量，這是個黑魔法慎用
總結
屬性查找順序：實例的【__dict__】------類的【__dict__】-----父類【__dict__】
如果搜索這些地方后沒有找到異常，先找到就立即返回
class Animal:
def shout(self):
print("Animal shouts")
class Cat(Animal):
def shout(self):
print("miao")
a = Animal()
a.shout() # Animal shouts
b = Cat()
b.shout() # miao
print(a.__dict__) # {}
print(b.__dict__) # {}
print(Animal.__dict__) # {'__module__': '__main__', 'shout': function Animal.shout at 0x017BC228>, '__dict__': attribute '__dict__' of 'Animal' objects>, '__weakref__': attribute '__weakref__' of 'Animal' objects>, '__doc__': None}
Cat類中shout為什么沒有打印Animal中shout的方法，方法被覆蓋了？
那子類如何打印父類的同命的方法
class Animal:
def shout(self):
print("Animal shouts")
class Cat(Animal):
def shout(self):
print("miao")
def shout(self):
print("super(): " , super())
print(super(Cat, self))
super().shout()
super(Cat,self).shout() # 等價于super().shout()
self.__class__.__base__.shout(self) #不推薦使用
a = Animal()
a.shout() # Animal shouts
b = Cat()
b.shout() # super(): super: class 'Cat'>, Cat object>>
# super: class 'Cat'>, Cat object>>
# Animal shouts
# Animal shouts
# Animal shouts
print(a.__dict__) # {}
print(b.__dict__) # {}
print(Animal.__dict__) # {'__module__': '__main__', 'shout': function Animal.shout at 0x019AC228>, '__dict__': attribute '__dict__' of 'Animal' objects>, '__weakref__': attribute '__weakref__' of 'Animal' objects>, '__doc__': None}
print(Cat.__dict__) # {'__module__': '__main__', 'shout': function Cat.shout at 0x019F6150>, '__doc__': None}
super(Cat,self).shout()的作用相當于
那對于類方法和靜態方法是否也同樣適用尼？
class Animal:
@classmethod
def class_method(cls):
print("class_method")
@staticmethod
def static_method():
print("static_methond_animal")
class Cat(Animal):
@classmethod
def class_method(cls):
super().class_method() # class_method
print("class_method_cat")
@staticmethod
def static_method(cls,self):
super(Cat,self).static_method()
print("static_method_cat")
b = Cat()
b.class_method() # class_method
# class_method_cat
b.static_method(Cat,b)
# static_methond_animal
# static_method_cat
這些方法都可以覆蓋，原理都一樣，屬性字典的搜索順序
看以下一段代碼，有沒有問題
class A:
def __init__(self,a):
self.a = a
class B(A):
def __init__(self,b,c):
self.b = b
self.c = c
def printv(self):
print(self.b)
print(self.a)
a = B(100,300)
print(a.__dict__) # {'b': 100, 'c': 300}
print(a.__class__.__bases__) # (class '__main__.A'>,)
a.printv() # 100
# AttributeError: 'B' object has no attribute 'a'
上例代碼
class A:
def __init__(self,a):
self.a = a
class B(A):
def __init__(self,b,c):
super().__init__(b+c)
# A.__init__(self,b+c)
self.b = b
self.c = c
def printv(self):
print(self.b)
print(self.a)
a = B(100,300)
print(a.__dict__) # {'a': 400, 'b': 100, 'c': 300}
print(a.__class__.__bases__) # (class '__main__.A'>,)
a.printv() # 100
# 400
作為好的習慣，如果父類定義了__init__方法，你就改在子類__init__中調用它【建議適用super（）方法調用】
那子類什么時候自動調用父類的【__init__】方法？
例子一：【B實例的初始化會自動調用基類A的__init__方法】
class A:
def __init__(self):
self.a1 = "a1"
self.__a2 = "a2"
print("A init")
class B(A):
pass
b = B() # A init
print(b.__dict__) # {'a1': 'a1', '_A__a2': 'a2'}
例子二：【B實例的初始化__init__方法不會自動調用父類的初始化__init__方法，需要手動調用】
class A:
def __init__(self):
self.a1 = "a1"
self.__a2 = "a2"
print("A init")
class B(A):
def __init__(self):
self.b1 = "b1"
self.__b2 = "b2"
print("b init")
#A.__init__(self)
b = B() # b init
print(b.__dict__) # {'b1': 'b1', '_B__b2': 'b2'}
那如何正確實例化？
class Animal:
def __init__(self,age):
print("Animal init")
self.age = age
def show(self):
print(self.age)
class Cat(Animal):
def __init__(self,age,weight):
#調用父類的__init__方法的順序 決定show方法的結果
super(Cat, self).__init__(age)
print("Cat init")
self.age = age + 1
self.weight = weight
a = Cat(10,5)
a.show() # Animal init
# Cat init
# 11
怎么直接將上例中所有的實例屬性改變為私有屬性？
class Animal:
def __init__(self,age):
print("Animal init")
self.__age = age
def show(self):
print(self.__age)
class Cat(Animal):
def __init__(self,age,weight):
#調用父類的__init__方法的順序 決定show方法的結果
super(Cat, self).__init__(age)
print("Cat init")
self.__age = age + 1
self.__weight = weight
def show(self):
print(self.__age)
a = Cat(10,5)
a.show() # Animal init
# Cat init
# 11
print(a.__dict__) # {'_Animal__age': 10, '_Cat__age': 11, '_Cat__weight': 5}
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