详解详细介绍l了Python类的继承

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 &#39;int&#39;>

s = Student(&#39;Bob&#39;, &#39;Male&#39;, 88)
print s  # <class &#39;main.Student&#39;>

print dir(123) # [&#39;abs&#39;, &#39;add&#39;, &#39;and&#39;, &#39;class&#39;, &#39;cmp&#39;, &#39;coerce&#39;, &#39;delattr&#39;, &#39;p&#39;, &#39;pmod&#39;, &#39;doc&#39;, &#39;float&#39;, &#39;floorp&#39;, &#39;format&#39;, &#39;getattribute&#39;, &#39;getnewargs&#39;, &#39;hash&#39;, &#39;hex&#39;, &#39;index&#39;, &#39;init&#39;, &#39;int&#39;, &#39;invert&#39;, &#39;long&#39;, &#39;lshift&#39;, &#39;mod&#39;, &#39;mul&#39;, &#39;neg&#39;, &#39;new&#39;, &#39;nonzero&#39;, &#39;oct&#39;, &#39;or&#39;, &#39;pos&#39;, &#39;pow&#39;, &#39;radd&#39;, &#39;rand&#39;, &#39;rp&#39;, &#39;rpmod&#39;, &#39;reduce&#39;, &#39;reduce_ex&#39;, &#39;repr&#39;, &#39;rfloorp&#39;, &#39;rlshift&#39;, &#39;rmod&#39;, &#39;rmul&#39;, &#39;ror&#39;, &#39;rpow&#39;, &#39;rrshift&#39;, &#39;rshift&#39;, &#39;rsub&#39;, &#39;rtruep&#39;, &#39;rxor&#39;, &#39;setattr&#39;, &#39;sizeof&#39;, &#39;str&#39;, &#39;sub&#39;, &#39;subclasshook&#39;, &#39;truep&#39;, &#39;trunc&#39;, &#39;xor&#39;, &#39;bit_length&#39;, &#39;conjugate&#39;, &#39;denominator&#39;, &#39;imag&#39;, &#39;numerator&#39;, &#39;real&#39;]

print dir(s) # [&#39;class&#39;, &#39;delattr&#39;, &#39;dict&#39;, &#39;doc&#39;, &#39;format&#39;, &#39;getattribute&#39;, &#39;hash&#39;, &#39;init&#39;, &#39;module&#39;, &#39;new&#39;, &#39;reduce&#39;, &#39;reduce_ex&#39;, &#39;repr&#39;, &#39;setattr&#39;, &#39;sizeof&#39;, &#39;str&#39;, &#39;subclasshook&#39;, &#39;weakref&#39;, &#39;gender&#39;, &#39;name&#39;, &#39;score&#39;, &#39;whoAmI&#39;]

print getattr(s, &#39;name&#39;) # Bob
setattr(s, &#39;name&#39;, &#39;Adam&#39;) 
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(&#39;Bob&#39;, &#39;Male&#39;, age=18, course=&#39;Python&#39;)
print p.age # 18
print p.course #Python

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