overriding a property

Peter Otten __peter__ at web.de
Wed Oct 20 16:09:12 CEST 2010


Lucasm wrote:

> On 19 Okt, 18:28, Steven D'Aprano <st... at REMOVE-THIS-
> cybersource.com.au> wrote:
>> On Tue, 19 Oct 2010 06:39:56 -0700, Lucasm wrote:
>> > Hi,
>>
>> > A question. Is it possible to dynamically override a property?
>>
>> > class A(object):
>> > @property
>> > def return_five(self):
>> > return 5
>>
>> > I would like to override the property for an instance of A to say the
>> > string 'bla'.
>> >>> class A(object):
>>
>> ...     _five = 5  # class attribute shared by all instances
>> ...     @property
>> ...     def return_five(self):
>> ...         return self._five
>> ...
>>
>> >>> a = A()
>> >>> a._five = 'bla'  # set an instance attribute
>> >>> b = A()
>> >>> print a.return_five
>> bla
>> >>> print b.return_five
>>
>> 5
>>
>> --
>> Steven
> 
> Thanks for the answers. I would like to override the property though
> without making special modifications in the main class beforehand. Is
> this possible?

You can dynamically change the instance's class:

>>> class A(object):
...     @property
...     def five(self): return 5
...
>>> a = A()
>>> b = A()
>>> class B(type(b)):
...     @property
...     def five(self): return "FIVE"
...
>>> b.__class__ = B
>>> a.five
5
>>> b.five
'FIVE'

But still -- what you are trying looks like a bad idea. What's your usecase?

Peter




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