Python类的继承(进阶5)

1. python中什么是继承

　　python中什么是继承:

新类不必从头编写
新类从现有的类继承，就自动拥有了现有类的所有功能
新类只需要编写现有类缺少的新功能

　　继承的好处：

复用已有代码
自动拥有了现有类的所有功能
只需要编写缺少的新功能

　　继承的特点：

子类和父类是is关系

　　python继承的特点：

总是从某个类继承
不要忘记调用super().init

2. python中继承一个类

 1 class Person(object):
 2     def __init__(self, name, gender):
 3         self.name = name
 4         self.gender = gender
 5 class Teacher(Person):
 6     def __init__(self, name, gender, course):
 7         super(Teacher, self).__init__(name, gender)
 8         self.course = course
 9 
10 t = Teacher('Alice', 'Female', 'English')
11 print t.name
12 print t.course

3. python中判断类型

　　函数isinstance()可以判断一个变量的类型，既可以用在Python内置的数据类型如str、list、dict，也可以用在我们自定义的类，它们本质上都是数据类型。

 1 class Person(object):
 2     def __init__(self, name, gender):
 3         self.name = name
 4         self.gender = gender
 5 
 6 class Student(Person):
 7     def __init__(self, name, gender, score):
 8         super(Student, self).__init__(name, gender)
 9         self.score = score
10 
11 class Teacher(Person):
12     def __init__(self, name, gender, course):
13         super(Teacher, self).__init__(name, gender)
14         self.course = course
15 
16 t = Teacher('Alice', 'Female', 'English')
17 
18 print isinstance(t, Person)
19 print isinstance(t, Student)
20 print isinstance(t, Teacher)
21 print isinstance(t, object)

4. python中多态

 1 class Person(object):
 2     def __init__(self, name, gender):
 3         self.name = name
 4         self.gender = gender
 5     def whoAmI(self):
 6         return 'I am a Person, my name is %s' % self.name
 7 
 8 class Student(Person):
 9     def __init__(self, name, gender, score):
10         super(Student, self).__init__(name, gender)
11         self.score = score
12     def whoAmI(self):
13         return 'I am a Student, my name is %s' % self.name
14 
15 class Teacher(Person):
16     def __init__(self, name, gender, course):
17         super(Teacher, self).__init__(name, gender)
18         self.course = course
19     def whoAmI(self):
20         return 'I am a Teacher, my name is %s' % self.name
21         
22         
23 import json
24 
25 class Students(object):
26     def read(self):
27         return r'["Tim", "Bob", "Alice"]'
28 
29 s = Students()
30 
31 print json.load(s)

5. python中多重继承

　　除了从一个父类继承外，Python允许从多个父类继承，称为多重继承。Java不能多继承

 1 class A(object):
 2     def __init__(self, a):
 3         print 'init A...'
 4         self.a = a
 5 
 6 class B(A):
 7     def __init__(self, a):
 8         super(B, self).__init__(a)
 9         print 'init B...'
10 
11 class C(A):
12     def __init__(self, a):
13         super(C, self).__init__(a)
14         print 'init C...'
15 
16 class D(B, C):
17     def __init__(self, a):
18         super(D, self).__init__(a)
19         print 'init D...'
20         
21         
22 class Person(object):
23     pass
24 
25 class Student(Person):
26     pass
27 
28 class Teacher(Person):
29     pass
30 
31 class SkillMixin(object):
32     pass
33 
34 class BasketballMixin(SkillMixin):
35     def skill(self):
36         return 'basketball'
37 
38 class FootballMixin(SkillMixin):
39     def skill(self):
40         return 'football'
41 
42 class BStudent(BasketballMixin):
43     pass
44 
45 class FTeacher(FootballMixin):
46     pass
47 
48 s = BStudent()
49 print s.skill()
50 
51 t = FTeacher()
52 print t.skill()

6. python中获取对象信息

　　除了用 isinstance() 判断它是否是某种类型的实例外，还有没有别的方法获取到更多的信息呢？

　　首先可以用 type() 函数获取变量的类型，它返回一个 Type 对象

　　dir() 函数获取变量的所有属性

　　dir()返回的属性是字符串列表，如果已知一个属性名称，要获取或者设置对象的属性，就需要用 getattr() 和 setattr( )函数了

 1 class Person(object):
 2     def __init__(self, name, gender):
 3         self.name = name
 4         self.gender = gender
 5 
 6 class Student(Person):
 7     def __init__(self, name, gender, score):
 8         super(Student, self).__init__(name, gender)
 9         self.score = score
10     def whoAmI(self):
11         return 'I am a Student, my name is %s' % self.name
12 
13 print type(123) # <type 'int'>
14 
15 s = Student('Bob', 'Male', 88)
16 print s  # <class '__main__.Student'>
17 
18 print dir(123) # ['__abs__', '__add__', '__and__', '__class__', '__cmp__', '__coerce__', '__delattr__', '__div__', '__divmod__', '__doc__', '__float__', '__floordiv__', '__format__', '__getattribute__', '__getnewargs__', '__hash__', '__hex__', '__index__', '__init__', '__int__', '__invert__', '__long__', '__lshift__', '__mod__', '__mul__', '__neg__', '__new__', '__nonzero__', '__oct__', '__or__', '__pos__', '__pow__', '__radd__', '__rand__', '__rdiv__', '__rdivmod__', '__reduce__', '__reduce_ex__', '__repr__', '__rfloordiv__', '__rlshift__', '__rmod__', '__rmul__', '__ror__', '__rpow__', '__rrshift__', '__rshift__', '__rsub__', '__rtruediv__', '__rxor__', '__setattr__', '__sizeof__', '__str__', '__sub__', '__subclasshook__', '__truediv__', '__trunc__', '__xor__', 'bit_length', 'conjugate', 'denominator', 'imag', 'numerator', 'real']
19 
20 print dir(s) # ['__class__', '__delattr__', '__dict__', '__doc__', '__format__', '__getattribute__', '__hash__', '__init__', '__module__', '__new__', '__reduce__', '__reduce_ex__', '__repr__', '__setattr__', '__sizeof__', '__str__', '__subclasshook__', '__weakref__', 'gender', 'name', 'score', 'whoAmI']
21 
22 print getattr(s, 'name') # Bob
23 setattr(s, 'name', 'Adam') 
24 print s.name # Adam
25 
26 class Person(object):
27 
28     def __init__(self, name, gender, **kw):
29         self.name = name
30         self.gender = gender
31         for k, v in kw.iteritems():
32             setattr(self, k, v)
33 
34 
35 p = Person('Bob', 'Male', age=18, course='Python')
36 print p.age # 18
37 print p.course #Python