零基础入门学习Python（19）：对象（4）组合、绑定

这节先介绍一下组合：即直接把需要的类放进另一种类中去实例化

>>> class Teacher:        def __init__(self,x):            self.teacher = x>>> class Student:        def __init__(self,y):            self.student = y>>> class School:        def __init__(self,x,y):            self.teacherSchool = Teacher(x)     #直接把需要的类放进去实例化            self.studentSchool = Student(y)        def printSchool(self):            print("The school has ",self.teacherSchool.teacher," teachers and ",self.studentSchool.student," students.")>>> school = School(10,100)>>> school.printSchool()The school has  10  teachers and  100  students.

再介绍一下类、类对象和实例对象

>>> class A:       #类        count = 0>>> a = A()        #类对象>>> b = A()>>> a.count        #类对象访问属性值即为类中属性的值0>>> b.count0>>> a.count += 10  #修改a对象属性值>>> a.count10>>> b.count0>>> A.count0>>> A.count += 100>>> b.count100>>> a.count        #a实例覆盖了类A中的count值10>>> class B:        def num(self):            print("num")>>> a = B()>>> a.num()num>>> a.num = 1      #实例化后的a创建了一个x属性>>> a.num1>>> a.num()        #如果属性名跟方法名相同，属性会覆盖方法，此时相当于调用不存在的方法，所以会出错Traceback (most recent call last):  File "<pyshell#47>", line 1, in <module>    a.num()TypeError: 'int' object is not callable

最后再介绍一下绑定：Python严格要求方法需要有实例才能被调用，这种限制其实就是Python所谓的绑定概念。

>>> class C:        def setXY(self,x,y):            self.x = x            self.y = y        def printXY(self):            print("x = ", self.x,"y = ", self.y)>>> c = C()>>> c.setXY(2,7)   >>> c.printXY()x =  2 y =  7>>> c.__dict__     #查看对象所拥有的属性，返回字典类型{'y': 7, 'x': 2}>>> C.__dict__     #属性值2和7仅属于对象cdict_proxy({'__module__': '__main__', 'printXY': <function printXY at 0x02699AE0>, 'setXY': <function setXY at 0x02148738>, '__dict__': <attribute '__dict__' of 'C' objects>, '__weakref__': <attribute '__weakref__' of 'C' objects>, '__doc__': None})>>> del C          #删除类之后，类的对象c的属性仍然存在>>> c.x2>>> c.y7

零基础入门学习Python（18）：对象（3）继承