python 面向对象六 动态添加方法 __slots__限制动态添加方法

一、动态添加属性

 >>> class Student(object):
     pass

 >>> st = Student()
 >>> st.name = 'Jack'
 >>> st.name
 'Jack'

二、动态给实例添加方法

 >>> from types import MethodType
 >>> class Student(object):
     pass

 >>> def set_age(self, age):
     self.age = age

 >>> st.set_age = MethodType(set_age, st)   # 给实例绑定一个方法
 >>> st.set_age(25)
 >>> st.age
 25

三、动态给类添加方法

 >>> class Student(object):
     pass

 >>> def set_score(self, score):
     self.score = score

 >>> Student.set_score = set_score
 >>> s1 = Student()
 >>> s1.set_score(100)
 >>> s1.score
 100
 >>> s2 = Student()
 >>> s2.set_score(50)
 >>> s2.score
 50

四、限制实例的属性 __slots__

 >>> class Student(object):
     __slots__ = ('name', 'age')   # 用tuple定义允许绑定对的属性名称

 >>> s = Student()
 >>> s.name = 'Jack'
 >>> s.age = 20
 >>> s.score = 100
 Traceback (most recent call last):
   File "<pyshell#53>", line 1, in <module>
     s.score = 100
 AttributeError: 'Student' object has no attribute 'score'

__slots__定义的属性仅对当前类实例起作用，对继承的子类是不起作用的：

 >>> class GraduateStudent(Student):
 ...     pass
 ...
 >>> g = GraduateStudent()
 >>> g.score = 9999

除非在子类中也定义__slots__，这样，子类实例允许定义的属性就是自身的__slots__加上父类的__slots__：

 >>> class GraduateStudent(Student):
     __slots__ = ('score', )

 >>> g = GraduateStudent()
 >>> g.score = 100
 >>> g.name = 'Mike'
 >>> g.age = 10
 >>> g.other = 'abc'
 Traceback (most recent call last):
   File "<pyshell#69>", line 1, in <module>
     g.other = 'abc'
 AttributeError: 'GraduateStudent' object has no attribute 'other'