add slots sample

Author: michaelliao

py3/oop_advance/use_slots.py

@@ -0,0 +1,21 @@
+#!/usr/bin/env python3
+# -*- coding: utf-8 -*-
+
+class Student(object):
+    __slots__ = ('name', 'age') # 用tuple定义允许绑定的属性名称
+
+class GraduateStudent(Student):
+    pass
+
+s = Student() # 创建新的实例
+s.name = 'Michael' # 绑定属性'name'
+s.age = 25 # 绑定属性'age'
+# ERROR: AttributeError: 'Student' object has no attribute 'score'
+try:
+    s.score = 99
+except AttributeError as e:
+    print('AttributeError:', e)
+
+g = GraduateStudent()
+g.score = 99
+print('g.score =', g.score)