setattr() on "object" instance

[Duncan Booth]

Ahmad Syukri b <syockit at gmail.com> wrote:

> On Mar 16, 1:21 pm, Sean DiZazzo <half.ital... at gmail.com> wrote:
>> Why is it that you can setattr() on an instance of a class that
>> inherits from "object", but you can't on an instance of "object"
>> itself?
>>
>> >>> o = object()
>> >>> setattr(o, "x", 1000)
>>
>> Traceback (most recent call last):
>>   File "<stdin>", line 1, in <module>
>> AttributeError: 'object' object has no attribute 'x'
> 
> I suppose you cannot set attributes to instances of any built-in
> classes, i.e. int(), list() etc.

No, there are some built-in types where you can set additional attributes: 
e.g. functions.

You can set additional attributes on any class which has a __dict__ 
attribute. When you subclass an existing type your new type will always 
have a __dict__ unless you define __slots__ and the base class did not 
already have a __dict__.



> Since all classes inherit from object, I suppose the definition can be
> as simple as 'class Object:pass', and assignment can be as simple as
> 'o.x = 1000'

Inheriting from object by default is only true if you are talking about 
Python 3.x.

-- 
Duncan Booth http://kupuguy.blogspot.com