封裝指的是將對象的狀態信息隱藏在對象內部，不允許外部直接訪問對象內部信息，而是通過該類提供的方法來實現對內部信息的操作和訪問；封裝的含義，實際上，是把該隱藏的隱藏起來，該暴露的暴露出來；Python只需要將類的成員名為以雙下划線開頭，就可以隱藏類中的成員。
一、封裝數據屬性
例：
class Fraction:
__grade = 0
def __init__(self,name):
self.__name = name
def setting_grade(self,var):
if isinstance(var,int) and var >= 0 and var <=100:
Fraction.__grade = var
else:
print ('請輸入正確的分數！')
def setting_name(self,set_name):
if isinstance(set_name,str):
self.__name = set_name
else:
print ('請輸入正確的姓名！')
def get_fraction(self):
print ('%s分數是：%s'%(self.__name,Fraction.__grade))
F = Fraction('小黃')
print (F.__grade) # 報錯 AttributeError: 'Fraction' object has no attribute '__grade'
print (F.__name) # 報錯 AttributeError: 'Fraction' object has no attribute '__name'
F.get_fraction() # 打印 小黃分數是：0
F.setting_name('小明')
F.setting_grade(100) # setting_grade()、setting_name()會對用戶設置grade、name進行控制，符合條件才能允許設置
F.get_fraction() # 打印 小明分數是：100
# 可以使用 _類名來訪問或修改對象的實例變量
print (F._Fraction__grade) # 打印 100
print (F._Fraction__name) # 打印 小明
上面例子中，代碼print (F.__grade)和print (F.__name)直接訪問私有變量會報錯setting_grade()、setting_name()方法用於對grade、name進行設置，只有符合條件才能允許設置；print (F._Fraction__grade)和print (F._Fraction__name)通過 _類名來訪問對象的實例變量（通常不要這么做），可以看出Python並沒有實現真正隱藏，只是改變以雙下划線開頭的變量，在這些變量前添加單下畫線和變量名。
二、封裝函數屬性
例：
class SumFraction:
def __init__(self,usually,test):
self.__usually = usually
self.__test = test
def set_usually_score(self,usually_var):
if isinstance(usually_var,int) and usually_var >= 0 and usually_var <=100:
self.__usually = usually_var
else:
print ('請輸入正確的分數！')
def set_test_score(self,test_var):
if isinstance(test_var,int) and test_var >= 0 and test_var <=100:
self.__test = test_var
else:
print ('請輸入正確的分數！')
def __calculation(self): # 私有方法，只能內部使用，對外部隱藏運算邏輯
return self.__usually * 0.3 + self.__test * 0.7
def final_grade(self):
return self.__calculation()
S = SumFraction(100,50)
print (S.final_grade()) # 打印 65.0
print (S.__calculation()) # 調用隱藏的__calculation()方法，會報錯 AttributeError: 'SumFraction' object has no attribute '__calculation'
print (S._SumFraction__calculation()) # 可以使用_類名方法名調用（不推薦這樣做），打印 65.0
# 修改__usually和__test
S.set_usually_score(70)
S.set_test_score(100)
print (S.final_grade()) # 通過final_grade()方法內部進行訪問__calculation()私有方法，打印 91.0
上面代碼中，set_usually_score()和set_test_score()用於對usually 、test進行設置；__calculation()是私有方法，默認是隱藏的，只允許內部使用，外部使用會報錯，當然也可以使用_類名方法名調用，但並不推薦這么做；print (S.final_grade())通過final_grade()方法內部訪問__calculation()私有方法。
三、property
先看一下幫助文檔：
>>> help(property) Help on class property in module builtins: class property(object) | property(fget=None, fset=None, fdel=None, doc=None) | | Property attribute. | | fget | function to be used for getting an attribute value | fset | function to be used for setting an attribute value | fdel | function to be used for del'ing an attribute | doc | docstring | | Typical use is to define a managed attribute x: | | class C(object): | def getx(self): return self._x | def setx(self, value): self._x = value | def delx(self): del self._x | x = property(getx, setx, delx, "I'm the 'x' property.") | | Decorators make defining new properties or modifying existing ones easy: | | class C(object): | @property | def x(self): | "I am the 'x' property." | return self._x | @x.setter | def x(self, value): | self._x = value | @x.deleter | def x(self): | del self._x | | Methods defined here: | | __delete__(self, instance, /) | Delete an attribute of instance. | | __get__(self, instance, owner, /) | Return an attribute of instance, which is of type owner. | | __getattribute__(self, name, /) | Return getattr(self, name). | | __init__(self, /, *args, **kwargs) | Initialize self. See help(type(self)) for accurate signature. | | __set__(self, instance, value, /) | Set an attribute of instance to value. | | deleter(...) | Descriptor to change the deleter on a property. | | getter(...) | Descriptor to change the getter on a property. | | setter(...) | Descriptor to change the setter on a property. | | ---------------------------------------------------------------------- | Static methods defined here: | | __new__(*args, **kwargs) from builtins.type | Create and return a new object. See help(type) for accurate signature. | | ---------------------------------------------------------------------- | Data descriptors defined here: | | __isabstractmethod__ | | fdel | | fget | | fset
@property 可以在一個類中把方法變成同名屬性調用，能用屬性的方式來訪問該屬性。
@x.setter 表示可寫，最大作用是用於限制屬性的定義，x是被@property修飾的方法名，@x.setter修飾的方法名@property修飾的方法名必須同名。
@x.deleter 表示可刪除，x是被@property修飾的方法名，@x.deleter修飾的方法名@property修飾的方法名必須同名。
例：
class SumFraction:
def __init__(self,value):
self.__score = value
@property # 讀
def score(self):
print ('讀......')
return self.__score
@score.setter # 寫
def score(self,var):
print ('寫......')
if isinstance(var,int) and var >= 0 and var <=100:
self.__score = var
return self.__score
else:
print ('請輸入正確的分數！')
return
@score.deleter # 刪除
def score(self):
print ("刪除self.__score......")
del self.__score
S = SumFraction(100)
S.score = 80 # 寫，打印 改......
print (S.score)
'''
讀，打印
讀......
80
'''
del S.score # 刪除，打印 刪除self.__score......
print (S.score) # __score已被刪除，打印 AttributeError: 'SumFraction' object has no attribute '_SumFraction__score'
用property類來實現，例：
class SumFraction:
def __init__(self,value):
self.__score = value
def get_score(self):
print ('讀......')
return self.__score
def set_score(self,var):
print ('寫......')
if isinstance(var,int) and var >= 0 and var <=100:
self.__score = var
return self.__score
else:
print ('請輸入正確的分數！')
return
def del_score(self):
print ("刪除self.__score......")
del self.__score
score = property(get_score,set_score,del_score,'這里是屬性含義~ ')
S = SumFraction(100)
S.score = 80 # 寫，打印 改......
print (S.score)
'''
讀，打印
讀......
80
'''
print (SumFraction.score.__doc__) # 屬性含義，打印 這里是屬性含義~
del S.score # 刪除，打印 刪除self.__score......
print (S.score) # __score已被刪除，打印 AttributeError: 'SumFraction' object has no attribute '_SumFraction__score'