二十二. Python基础(22)--继承
● 知识框架
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● 继承关系中self的指向
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当一个对象调用一个方法时，这个方法的self形参会指向这个对象 |
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class A: def get(self): self.say()
def say(self): print('AAAAA')
class B(A): def say(self): print('BBBBB')
b = B() b.get() # BBBBB # 当一个对象调用一个方法时，这个方法中的self就指向这个对象 # 子类先调用自己的属性或方法, 子类自己没有才调父类的 # 如果是class B(A):pass, 那么结果是'AAAAA' |
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print(dir(b)) # ['__class__', '__delattr__', '__dict__', '__dir__', '__doc__', '__eq__', '__format__', '__ge__', '__getattribute__', '__gt__', '__hash__', '__init__', '__init_subclass__', '__le__', '__lt__', '__module__', '__ne__', '__new__', '__reduce__', '__reduce_ex__', '__repr__', '__setattr__', '__sizeof__', '__str__', '__subclasshook__', '__weakref__', 'cls_att', 'get', 'name', 'say'] print(b.__dict__) # {'name': 'Arroz'} print(vars(b)) # {'name': 'Arroz'} print(b.__class__) # <class '__main__.B'> print(B.__class__) #<class 'type'> # 实例关系 print(B.__bases__) # (<class '__main__.A'>,) # 继承关系 print(B.__doc__) # This is class B |
● 经典类(old-style)和新式(new-style)类调用父类方法的区别
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class Dog(Animal): def __init__(self, name): # Animal.__init__(self, name) # 经典类, 注意不要遗漏self super().__init__(name) # 新式类, 等价于super(Dog, self).__init__(name),读作"调用Dog的父类 的方法(calling Dog's parent's method)" |
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内置函数super([type[, object-or-type]]) Return a proxy object that delegates method calls to a parent or sibling class of type. This is useful for accessing inherited methods that have been overridden in a class. The search order is same as that used by getattr() except that the type itself is skipped. |
● 综合案例
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class Base: cls_attr = 'class attribute' def __init__(self, name, age, job): self.name = name self.age = age self.job = job def bmeth(self): print('Base method')
class Derived_0(Base): def dmeth(self): print('Derived method')
print(type(Base)) # <class 'type'>, 元类 print(type(Derived_0)) # <class 'type'>, 元类
# 没有添加新的对象属性, 不用使用super() d_0 = Derived_0('Paul', 55, 'Singer') print(d_0.job)
# 下面添加了添加了新的对象属性, 需要使用super() class Derived_1(Base): def __init__(self, name, age, job, hobby): super(Derived_1, self).__init__(name, age,job) # ※ self.hobby = hobby def dmeth(self): print('Derived method') def show(self): print(self.name, self.age, self.job,self.hobby)
class Derived_2(Base): def __init__(self, name, hobby): super(Derived_2, self).__init__(name, 20, 'teacher') # 子类调用父类方法时, 参数的个数不能缺少, 并且可以把已知的属性先传给父类的构造函数 self.hobby = hobby def dmeth(self): print('Derived method') def show(self): print(self.name, self.age, self.job,self.hobby)
class Derived_3(Base): def __init__(self, hobby): super(Derived_3, self).__init__("Paul", 22, 'painter') # 子类调用父类方法时, 参数的个数不能缺少, 并且可以把已知的属性先传给父类的构造函数 self.hobby = hobby
def dmeth(self): print('Derived method')
def show(self): print(self.name, self.age, self.job, self.hobby)
#① ####################################################### b = Base('Arroz', 18, 'teacher') print(Base.__dict__) # 类的属性 ''' {'__module__': '__main__', 'cls_attr': 'class attribute', '__init__': <function Base.__init__ at 0x00000000028EA840>, 'bmeth': <function Base.bmeth at 0x00000000028EA8C8>, '__dict__': <attribute '__dict__' of 'Base' objects>, '__weakref__': <attribute '__weakref__' of 'Base' objects>, '__doc__': None} ''' print(b.__dict__) # 对象属性 ''' {'name': 'Arroz', 'age': 18, 'job': 'teacher'} ''' print('----------------------') #② ####################################################### d_1 = Derived_1('Arroz', 18, 'teacher','swimming') d_1.show() # Arroz 18 teacher swimming print('----------------------') #③ ####################################################### d_2 = Derived_2('Pwter', 'skating') d_2.show() # Pwter 20 teacher skating print('----------------------') #④ ####################################################### d_3 = Derived_3('jogging') d_3.show() # Paul 22 painter jogging |