Python面向对象编程（2）——深入类的属性

2019-11-06 07:38:13

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2 深入类的属性2.1 同名的类属性与实例属性在使用实例名.属性名应用时，优先引用实例属性使用类名.属性名时，只能引用类属性classClassAttrDemo1: a=10 def__init__(self): self.a=20 self.b=20 cad1=ClassAttrDemo1()PRint("example attribute:",cad1.a)print("class attribute:",ClassAttrDemo1.a)print("error:",ClassAttrDemo1.b)

2.2%20属性访问的特殊方法（反射） %20 %20 字符串操作类的属性/方法 %20 %20 主要工具函数：has_attr(obj_name,'属性')、set_attr(obj_name,'属性','值')、get_attr(obj_name,'属性','值')classClassAttrDemo1: %20a=10 def__init__(self): self.a=20 self.b=20 cad1=ClassAttrDemo1()#%20print("example%20attribute:",cad1.a)#%20print("class%20attribute:",ClassAttrDemo1.a)#print("error:",ClassAttrDemo1.b)print("example%20attribute%20value:",getattr(cad1,'a'))setattr(cad1,'a',80)print("changed%20attribute%20value:",getattr(cad1,'a'))print("attributexit:",hasattr(cad1,'c'));2.3 属性包装将方法包装为属性，隐藏相关实现（控制属性类型或范围、虚拟属性）三种属性操作：@property（可读）、@<property-name>.setter（可写）、@<property-name>.delete（可删除）# -*- coding:utf-8 -*-classWasher: def__init__(self,water=10,scour=2): self._water=water#_water为私有属性 self.scour=scour self.year=2012 #方法包装为属性 @property defwater(self): returnself._water #可写 @water.setter defwater(self,water): if0<water<200: self._water=water else: print("set water failure...") #虚拟属性 @property deftotal_year(self): return2017-self.year defset_water(self,water): self.water=water defset_scour(self,scour): self.scour=scour defadd_water(self): print("add water:",self.water) defadd_scour(self): print("add scour:",self.scour) defstart_wash(self): self.add_water() self.add_scour() print("start wash ...") if__name__ =='__main__': w=Washer(20,5) print(w.water) w.water=25 print(w.water) w.water=222 print(w.water) print(w.total_year)2.4 描述符实现特殊协议方法的类作为另一个类的类属性拦截和控制属性访问，并且可以重复使用特殊协议方法如下：__set__()、__get__()、__delete__()classNonNegative: def__init__(self,default=0): self.default=default def__set__(self,instance,val): ifval>=0: self.default=val else: print("The value must be positive") def__get__(self,instance,owner): returnself.default def__delete__(self,instance): passclassMovie: rating=NonNegative() price=NonNegative() def__init__(self): passif__name__ =='__main__': m=Movie() print(m.rating) m.price=10 print(m.price) m.price=-5 print(m.price)