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

class Person(object):
    def __init__(self, name, gender):
        self.name = name
        self.gender = gender
class Teacher(Person):
    def __init__(self, name, gender, course):
        super(Teacher, self).__init__(name, gender)
        self.course = course

t = Teacher('Alice', 'Female', 'English')
print t.name
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。

class Person(object):
    def __init__(self, name, gender):
        self.name = name
        self.gender = gender

class Student(Person):
    def __init__(self, name, gender, score):
        super(Student, self).__init__(name, gender)
        self.score = score

class Teacher(Person):
    def __init__(self, name, gender, course):
        super(Teacher, self).__init__(name, gender)
        self.course = course

t = Teacher('Alice', 'Female', 'English')

print isinstance(t, Person)
print isinstance(t, Student)
print isinstance(t, Teacher)
print isinstance(t, object)

4. python中多态

class Person(object):
    def __init__(self, name, gender):
        self.name = name
        self.gender = gender
    def whoAmI(self):
        return 'I am a Person, my name is %s' % self.name

class Student(Person):
    def __init__(self, name, gender, score):
        super(Student, self).__init__(name, gender)
        self.score = score
    def whoAmI(self):
        return 'I am a Student, my name is %s' % self.name

class Teacher(Person):
    def __init__(self, name, gender, course):
        super(Teacher, self).__init__(name, gender)
        self.course = course
    def whoAmI(self):
        return 'I am a Teacher, my name is %s' % self.name
        
        
import json

class Students(object):
    def read(self):
        return r'["Tim", "Bob", "Alice"]'

s = Students()

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

class A(object):
    def __init__(self, a):
        print 'init A...'
        self.a = a

class B(A):
    def __init__(self, a):
        super(B, self).__init__(a)
        print 'init B...'

class C(A):
    def __init__(self, a):
        super(C, self).__init__(a)
        print 'init C...'

class D(B, C):
    def __init__(self, a):
        super(D, self).__init__(a)
        print 'init D...'
        
        
class Person(object):
    pass

class Student(Person):
    pass

class Teacher(Person):
    pass

class SkillMixin(object):
    pass

class BasketballMixin(SkillMixin):
    def skill(self):
        return 'basketball'

class FootballMixin(SkillMixin):
    def skill(self):
        return 'football'

class BStudent(BasketballMixin):
    pass

class FTeacher(FootballMixin):
    pass

s = BStudent()
print s.skill()

t = FTeacher()
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

class Person(object):
    def __init__(self, name, gender):
        self.name = name
        self.gender = gender

class Student(Person):
    def __init__(self, name, gender, score):
        super(Student, self).__init__(name, gender)
        self.score = score
    def whoAmI(self):
        return 'I am a Student, my name is %s' % self.name

print type(123) # <type 'int'>

s = Student('Bob', 'Male', 88)
print s  # <class '__main__.Student'>

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']

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']

print getattr(s, 'name') # Bob
setattr(s, 'name', 'Adam') 
print s.name # Adam

class Person(object):

    def __init__(self, name, gender, **kw):
        self.name = name
        self.gender = gender
        for k, v in kw.iteritems():
            setattr(self, k, v)


p = Person('Bob', 'Male', age=18, course='Python')
print p.age # 18
print p.course #Python