6.3 多态
7. 类相关函数
- issubclass：检测一个类是否是另一个类的子类
- isinstance：检测一个对象是否是一个类的实例
- hasattr：检测一个对象是否有成员xxx
- getattr：get attribute
- setattr：set attribute
- delattr：delete attribute
- dir：获取对象的成员列表
class A():
pass
class B(A):
pass
class C(B,A):
pass
print(A.__mro__)
print(B.__mro__)
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(<class '__main__.A'>, <class 'object'>)
(<class '__main__.B'>, <class '__main__.A'>, <class 'object'>)
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# 多继承的例子
# 子类可以直接拥有父类的属性和方法，私有属性和方法除外
class Fish():
def __init__(self, name):
self.name = name
def swim(self):
print("I am swimming......")
class Bird():
def __init__(self, name):
self.name = name
def fly(self):
print("I am flying.....")
class Person():
def __init__(self, name):
self.name = name
def worked(self):
print("Working......")
class SuperMan(Person, Bird, Fish):
def __init__(self, name):
self.name = name
s = SuperMan("a")
s.fly()
s.swim()
s.worked()
# 单继承的例子
class Student(Person):
def __init__(self, name):
self.name = name
stu = Student("a")
stu.worked()
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I am flying.....
I am swimming......
Working......
Working......
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# 菱形继承问题
class A():
pass
class B(A):
pass
class C(A):
pass
class D(B,C):
pass
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# 构造函数例子
class Person():
# 对Person类进行实例化的时候
# 姓名要确定
# 年龄得确定
# 地址肯定有
def __init__(self):
self.name = "NoName"
self.age = 18
self.address = "Studentwhonheim"
print("In init func")
# 实例化一个人
p = Person()
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In init func
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# 构造函数的调用顺序 - 1
# 如果子类没有写构造函数，则自动向上查找，直到找到为止
class A():
def __init__(self):
print("A")
class B(A):
def __init__(self):
print("B")
class C(B):
pass
# 此时，首先C的构造函数
# 如果没有，则向上按照MRO顺序查找父类的构造函数，直到找到为止
c = C()
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A
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# 构造函数的调用顺序 - 2
class A():
def __init__(self):
print("A")
class B(A):
def __init__(self, name):
print("B")
print(name)
class C(B):
pass
# 此时，首先C的构造函数
# 如果没有，则向上按照MRO顺序查找父类的构造函数，直到找到为止
# 此时，会出现参数结构不对应错误
c = C()
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---------------------------------------------------------------------------
TypeError Traceback (most recent call last)
<ipython-input-11-40c74f7fff64> in <module>
14 # 如果没有，则向上按照MRO顺序查找父类的构造函数，直到找到为止
15 # 此时，会出现参数结构不对应错误
---> 16 c = C()
TypeError: __init__() missing 1 required positional argument: 'name'
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# 构造函数的调用顺序 - 3
class A():
def __init__(self):
print("A")
class B(A):
def __init__(self, name):
print("B")
print(name)
class C(B):
# C中想扩展B的构造函数
# 即调用B的构造函数后再添加一些功能
# 有两种方法实现
'''
# 第一种是通过父类名调用
def __init__(self, name):
# 首先调用父类构造函数
B.__init__(self, name)
# 其次，再增加自己的功能
print("这是C中附加的功能")
'''
# 第二种，使用super调用
def __init__(self, name):
# 首先调用父类构造函数
super(C, self).__init__(name)
# 其次，再增加自己的功能
print("这是C中附加的功能")
# 此时，首先C的构造函数
# 如果没有，则向上按照MRO顺序查找父类的构造函数，直到找到为止
# 此时，会出现参数结构不对应错误
c = C("我是C")
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B
我是C
这是C中附加的功能
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# Mixin案例
class Person():
name = "ruochen"
age = 18
def eat(self):
print("EAT......")
def drink(self):
print("DRINK......")
def sleep():
print("SLEEP......")
class Teacher(Person):
def work(self):
print("Work")
class Student(Person):
def study(self):
print("Study")
class Tutor(Teacher, Student):
pass
t = Tutor()
print(Tutor.__mro__)
print(t.__dict__)
print(Tutor.__dict__)
print("*" * 20)
class TeacherMixin():
def work(self):
print("Work")
class StudentMixin():
def study(self):
print("Study")
class TutorM(Person, TeacherMixin, StudentMixin):
pass
tt = TutorM()
print(TutorM.__mro__)
print(tt.__dict__)
print(TutorM.__dict__)
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(<class '__main__.Tutor'>, <class '__main__.Teacher'>, <class '__main__.Student'>, <class '__main__.Person'>, <class 'object'>)
{}
{'__module__': '__main__', '__doc__': None}
********************
(<class '__main__.TutorM'>, <class '__main__.Person'>, <class '__main__.TeacherMixin'>, <class '__main__.StudentMixin'>, <class 'object'>)
{}
{'__module__': '__main__', '__doc__': None}
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# issubclass
class A():
pass
class B(A):
pass
class C():
pass
print(issubclass(B, A))
print(issubclass(C, A))
print(issubclass(C, object))
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True
False
True
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# isinstance
class A():
pass
a = A()
print(isinstance(a, A))
print(isinstance(A, A))
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True
False
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# hasattr
class A():
name = "NoName"
a = A()
print(hasattr(a, "name"))
print(hasattr(a, "age"))
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True
False
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# help案例
# 我想知道setattr的具体用法
help(setattr)
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Help on built-in function setattr in module builtins:
setattr(obj, name, value, /)
Sets the named attribute on the given object to the specified value.
setattr(x, 'y', v) is equivalent to ``x.y = v''
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# dir 案例
class A():
pass
# dir(A)
a = A
dir(a)
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['__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__']
