封装指的是将对象的状态信息隐藏在对象内部，不允许外部直接访问对象内部信息，而是通过该类提供的方法来实现对内部信息的操作和访问；封装的含义，实际上，是把该隐藏的隐藏起来，该暴露的暴露出来；Python只需要将类的成员名为以双下划线开头，就可以隐藏类中的成员。
一、封装数据属性
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 ('请输入正确的分数！')
def setting_name(self,set_name):
if isinstance(set_name,str):
self.__name = set_name
else:
print ('请输入正确的姓名！')
def get_fraction(self):
print ('%s分数是：%s'%(self.__name,Fraction.__grade))
F = Fraction('小黄')
print (F.__grade) # 报错 AttributeError: 'Fraction' object has no attribute '__grade'
print (F.__name) # 报错 AttributeError: 'Fraction' object has no attribute '__name'
F.get_fraction() # 打印 小黄分数是：0
F.setting_name('小明')
F.setting_grade(100) # setting_grade()、setting_name()会对用户设置grade、name进行控制，符合条件才能允许设置
F.get_fraction() # 打印 小明分数是：100
# 可以使用 _类名来访问或修改对象的实例变量
print (F._Fraction__grade) # 打印 100
print (F._Fraction__name) # 打印 小明
上面例子中，代码print (F.__grade)和print (F.__name)直接访问私有变量会报错setting_grade()、setting_name()方法用于对grade、name进行设置，只有符合条件才能允许设置；print (F._Fraction__grade)和print (F._Fraction__name)通过 _类名来访问对象的实例变量（通常不要这么做），可以看出Python并没有实现真正隐藏，只是改变以双下划线开头的变量，在这些变量前添加单下画线和变量名。
二、封装函数属性
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 ('请输入正确的分数！')
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 ('请输入正确的分数！')
def __calculation(self): # 私有方法，只能内部使用，对外部隐藏运算逻辑
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()) # 调用隐藏的__calculation()方法，会报错 AttributeError: 'SumFraction' object has no attribute '__calculation'
print (S._SumFraction__calculation()) # 可以使用_类名方法名调用（不推荐这样做），打印 65.0
# 修改__usually和__test
S.set_usually_score(70)
S.set_test_score(100)
print (S.final_grade()) # 通过final_grade()方法内部进行访问__calculation()私有方法，打印 91.0
上面代码中，set_usually_score()和set_test_score()用于对usually 、test进行设置；__calculation()是私有方法，默认是隐藏的，只允许内部使用，外部使用会报错，当然也可以使用_类名方法名调用，但并不推荐这么做；print (S.final_grade())通过final_grade()方法内部访问__calculation()私有方法。
三、property
先看一下帮助文档：
>>> 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 可以在一个类中把方法变成同名属性调用，能用属性的方式来访问该属性。
@x.setter 表示可写，最大作用是用于限制属性的定义，x是被@property修饰的方法名，@x.setter修饰的方法名@property修饰的方法名必须同名。
@x.deleter 表示可删除，x是被@property修饰的方法名，@x.deleter修饰的方法名@property修饰的方法名必须同名。
例：
class SumFraction:
def __init__(self,value):
self.__score = value
@property # 读
def score(self):
print ('读......')
return self.__score
@score.setter # 写
def score(self,var):
print ('写......')
if isinstance(var,int) and var >= 0 and var <=100:
self.__score = var
return self.__score
else:
print ('请输入正确的分数！')
return
@score.deleter # 删除
def score(self):
print ("删除self.__score......")
del self.__score
S = SumFraction(100)
S.score = 80 # 写，打印 改......
print (S.score)
'''
读，打印
读......
80
'''
del S.score # 删除，打印 删除self.__score......
print (S.score) # __score已被删除，打印 AttributeError: 'SumFraction' object has no attribute '_SumFraction__score'
用property类来实现，例：
class SumFraction:
def __init__(self,value):
self.__score = value
def get_score(self):
print ('读......')
return self.__score
def set_score(self,var):
print ('写......')
if isinstance(var,int) and var >= 0 and var <=100:
self.__score = var
return self.__score
else:
print ('请输入正确的分数！')
return
def del_score(self):
print ("删除self.__score......")
del self.__score
score = property(get_score,set_score,del_score,'这里是属性含义~ ')
S = SumFraction(100)
S.score = 80 # 写，打印 改......
print (S.score)
'''
读，打印
读......
80
'''
print (SumFraction.score.__doc__) # 属性含义，打印 这里是属性含义~
del S.score # 删除，打印 删除self.__score......
print (S.score) # __score已被删除，打印 AttributeError: 'SumFraction' object has no attribute '_SumFraction__score'