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Re: why the attribute be deleted still in dir(man)?

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  Re: why the attribute be deleted still in dir(man)? Ian Kelly <ian.g.kelly@gmail.com> - 2014-08-23 17:22 -0600

#76914 — Re: why the attribute be deleted still in dir(man)?

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On Sat, Aug 23, 2014 at 4:49 PM, luofeiyu <elearn2014@gmail.com> wrote:
>
> class Person(object):
>        def addProperty(self, attribute):
>               getter = lambda self: self._getProperty(attribute)
>               setter = lambda self, value: self._setProperty(attribute,
value)
>               deletter = lambda self:self.delProperty(attribute)
>               setattr(self.__class__, attribute,
property(fget=getter,fset=setter,fdel=deletter,doc="Auto-generated method"))
>        def _setProperty(self, attribute, value):
>              setattr(self, '_' + attribute, value.title())
>       def _getProperty(self, attribute):
>             return getattr(self, '_' + attribute)
>       def delProperty(self,attribute):
>             delattr(self,'_' + attribute)

Unless you're going to have the property actually do something, this is
silly and useless.  Just use a normal attribute.

Even if this is really what you want to do, it's bad design. The class
defines the instances. You shouldn't have an instance method modifying the
structure of other instances of the class.

> >>> man.delProperty("name")
> >>> man.name
> Traceback (most recent call last):
>   File "<stdin>", line 1, in <module>
>   File "<stdin>", line 4, in <lambda>
>   File "<stdin>", line 12, in _getProperty
> AttributeError: 'Person' object has no attribute '_name'
> >>> dir(man)
> ['__class__', '__delattr__', '__dict__', '__dir__', '__doc__', '__eq__',
'__form
> at__', '__ge__', '__getattribute__', '__gt__', '__hash__', '__init__',
'__le__',
>  '__lt__', '__module__', '__ne__', '__new__', '__reduce__',
'__reduce_ex__', '__
> repr__', '__setattr__', '__sizeof__', '__str__', '__subclasshook__',
'__weakref_
> _', '_getProperty', '_setProperty', 'addProperty', 'delProperty', 'name']

You deleted the _name attribute where you're storing the value of the name
property. You didn't delete the name property, which is part of the class,
not the instance.

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