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’