Python類的繼承(進階5)

 

1. python中什么是繼承

　　python中什么是繼承:

• 新類不必從頭編寫
• 新類從現有的類繼承，就自動擁有了現有類的所有功能
• 新類只需要編寫現有類缺少的新功能

　　繼承的好處：

• 復用已有代碼
• 自動擁有了現有類的所有功能
• 只需要編寫缺少的新功能

　　繼承的特點：

• 子類和父類是is關系

　　python繼承的特點：

• 總是從某個類繼承
• 不要忘記調用super().init

2. python中繼承一個類

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中判斷類型

　　函數isinstance()可以判斷一個變量的類型，既可以用在Python內置的數據類型如str、list、dict，也可以用在我們自定義的類，它們本質上都是數據類型。

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中多態

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中多重繼承

　　除了從一個父類繼承外，Python允許從多個父類繼承，稱為多重繼承。Java不能多繼承

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中獲取對象信息

　　除了用 isinstance() 判斷它是否是某種類型的實例外，還有沒有別的方法獲取到更多的信息呢？

　　首先可以用 type() 函數獲取變量的類型，它返回一個 Type 對象

　　dir() 函數獲取變量的所有屬性

　　dir()返回的屬性是字符串列表，如果已知一個屬性名稱，要獲取或者設置對象的屬性，就需要用 getattr() 和 setattr( )函數了

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