Python面向對象編程（2）——深入類的屬性

2019-11-06 07:38:13

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2 深入類的屬性2.1 同名的類屬性與實例屬性在使用實例名.屬性名應用時，優先引用實例屬性使用類名.屬性名時，只能引用類屬性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屬性訪問的特殊方法（反射） %20 %20 字符串操作類的屬性/方法 %20 %20 主要工具函數：has_attr(obj_name,'屬性')、set_attr(obj_name,'屬性','值')、get_attr(obj_name,'屬性','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 屬性包裝將方法包裝為屬性，隱藏相關實現（控制屬性類型或范圍、虛擬屬性）三種屬性操作：@property（可讀）、@<property-name>.setter（可寫）、@<property-name>.delete（可刪除）# -*- coding:utf-8 -*-classWasher: def__init__(self,water=10,scour=2): self._water=water#_water為私有屬性 self.scour=scour self.year=2012 #方法包裝為屬性 @property defwater(self): returnself._water #可寫 @water.setter defwater(self,water): if0<water<200: self._water=water else: print("set water failure...") #虛擬屬性 @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 描述符實現特殊協議方法的類作為另一個類的類屬性攔截和控制屬性訪問，并且可以重復使用特殊協議方法如下：__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)