Python 限制属性的创建/设置
如何在类/子类之外限制属性的创建Python 限制属性的创建/设置,python,python-3.x,Python,Python 3.x,如何在类/子类之外限制属性的创建 __all__ = ["Employee","Salary","Wage"] ################################################################################################## class Person(object): def __init__(self,fname,lname,gender): self.__setfname(fname)
__all__ = ["Employee","Salary","Wage"]
##################################################################################################
class Person(object):
def __init__(self,fname,lname,gender):
self.__setfname(fname) # "We are all adults." vs. "Name mangling."
self.__setlname(lname)
self.__setgender(gender)
def __setfname(self,fname): self.__fname = fname
def __setlname(self,lname): self.__lname = lname
def __setgender(self,gender): self.__gender = gender
def getname(self): return "{} {}".format(self.__fname,self.__lname)
def getformattedname(self):
if(self.__gender.lower() == "m"):
return "Mr. {}".format(self.getname())
if(self.__gender.lower() == "f"):
return "Ms. {}".format(self.getname())
if(self.__gender.lower() == ""):
return "{}".format(self.getname())
class Payment(object):
def __init__(self,amount,currency="INR"): # currency="USD"
self.__setamount(amount)
self.__setcurrency(currency)
def __setamount(self,amount): self.__amount = amount
def __setcurrency(self,currency): self.__currency = currency
def getamount(self): return "{}".format(self.__amount)
def getformattedamount(self): return "{} {}".format(self.getamount(),self.__currency)
##################################################################################################
##################################################################################################
class Employee(Person):
def __init__(self,fname,lname,gender): super(Employee,self).__init__(fname,lname,gender)
def __str__(self): return self.getformattedname()
class Salary(Payment):
def __init__(self,amount,currency="INR"): super(Salary,self).__init__(amount,currency)
def __str__(self): return self.getformattedamount()
class Wage(Payment):
def __init__(self,amount,currency="INR"): super(Wage,self).__init__(amount,currency)
def __str__(self): return self.getformattedamount()
##################################################################################################
我同意这一点:
e1._Person__fname = "Spam"
s1._Payment__amount = "1000000000000000"
但以下代码创建了新属性:
e1.fname = "New"
s1.amount = -10
class Person(object):
__slots__ = ('_Person__fname', '_Person__lname', '_Person__gender')
...
class Employee(Person):
__slots__ = () # All subclasses also need define __slots__
...
e1._Person__fname = "Spam" # Fine
e1.fname = "New" # AttributeError: 'Employee' object has no attribute 'fname'
您可以这样做:
class A:
def __setattr__(self, attr, val):
try :
class_name, varname = attr.split('__', 1)
if class_name == '_' + self.__class__.__name__:
self.__dict__[attr] = val
else:
raise AttributeError
except ValueError:
raise AttributeError
演示:
>>> %run so.py
>>> a = A()
>>> a._A__foo = 1
>>> a._A__bar = 2
>>> a._A = 2
Traceback (most recent call last):
File "<ipython-input-28-eace128dbfc5>", line 1, in <module>
a._A = 2
File "/home/monty/py/so.py", line 10, in __setattr__
raise AttributeError
AttributeError
>>> a.A__bar = 2
Traceback (most recent call last):
File "<ipython-input-29-57210782cd6a>", line 1, in <module>
a.A__bar = 2
File "/home/monty/py/so.py", line 8, in __setattr__
raise AttributeError
AttributeError
>>> a._A__spam = 3
>>> a.__dict__
{'_A__foo': 1, '_A__spam': 3, '_A__bar': 2}
>>%运行so.py
>>>a=a()
>>>a.。u a_uufoo=1
>>>a.。\u a\u条=2
>>>a._a=2
回溯(最近一次呼叫最后一次):
文件“”,第1行,在
a、 _a=2
文件“/home/monty/py/so.py”,第10行,在__
提高属性错误
属性错误
>>>a.a____bar=2
回溯(最近一次呼叫最后一次):
文件“”,第1行,在
a、 a_uuu条=2
文件“/home/monty/py/so.py”,第8行,在__
提高属性错误
属性错误
>>>a.。\u a\u垃圾邮件=3
>>>格言__
{u-A-u-foo':1,'u-A-u-spam':3,'u-A-u-bar':2}
我们可以,尽管\uuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuu
e1.fname = "New"
s1.amount = -10
class Person(object):
__slots__ = ('_Person__fname', '_Person__lname', '_Person__gender')
...
class Employee(Person):
__slots__ = () # All subclasses also need define __slots__
...
e1._Person__fname = "Spam" # Fine
e1.fname = "New" # AttributeError: 'Employee' object has no attribute 'fname'
请注意,使用\uuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuu
时,实例的\uuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuu
class Foo(object):
def __init__(self):
self._amount = 0
@property
def amount(self):
return self._amount
f = Foo()
print f.amount # ok
f.amount = 100 # error
不要试图这样做。别人对你的课做什么不关你的事。您应该记录哪些属性应该可用,如果有人想滥用它,那是他们的问题,而不是你的问题
“我们在这里都是同意的成年人”是python的哲学。为什么额外的属性是一个问题?我使用\uu
前缀使属性私有化。我不希望这些“名称”(属性)在类外可以访问。(y)@“别人对你的类做什么不关你的事。”但是。。。如果其他人开始滥用这些属性,使模型/数据库开始受到影响,这是我的事。我和Daniel的观点相同。如果你买了一辆车,并以这样一种方式操纵刹车,使其不再工作,这几乎不是汽车制造商的问题,而是你自己的问题。如果您使用某个库的未记录功能,而突然这些功能不再受支持,那么这是您的事,而不是库作者的事。如果用户滥用你的代码,那是他的事,不是你的事。“仅按预期使用代码”。就我的两分钱。@GLES你的同事真的不值得信任吗?你不能指望他们不入侵数据库吗?@GLES:如果他们想入侵数据库,他们当然可以修改你的类的源代码?另外,object.\uuuuu setattr\uuuuuuu(您的类实例'which\u key\u i\u like',value)
将破坏您尝试的任何操作。谢谢!我迫切需要这样一种技巧,建议使用一种神奇的方法。@GLES:请在使用此解决方案之前阅读。谢谢!我要试试这个。我忽略了“装饰者”这个主题:)现在我意识到它忽略了我:)