can't set attributes of built-in/extension type

[Neal Becker]

Steve Holden wrote:

> Neal Becker wrote:
>> 7stud wrote:
>> 
>>> On Feb 21, 11:19 am, Neal Becker <ndbeck... at gmail.com> wrote:
>>>> I'm working on a simple extension.  Following the classic 'noddy'
>>>> example.
>>>>
>>>> In [15]: cmplx_int32
>>>> Out[15]: <type 'numpy.cmplx_int32'>
>>>>
>>>> Now I want to add an attribute to this type.  More precisely, I want a
>>>> class attribute.
>>>>
>>>> cmplx_int32.test = 0
>>>> ---------------------------------------------------------------------------
>>>> TypeError                                 Traceback (most recent call
>>>> last)
>>>>
>>>> /home/nbecker/numpy/<ipython console> in <module>()
>>>>
>>>> TypeError: can't set attributes of built-in/extension
>>>> type 'numpy.cmplx_int32'
>>>>
>>>> What am I missing?
>>>
>>> class Dog(object):
>>>     def __setattr__(self, attr, val):
>>>         print "TypeError: can't set attributes of built-in/extension"
>>>         print "type 'Dog.cmplx_int32'"
>>>
>>> d = Dog()
>>> d.test = 0
>>>
>>> --output:--
>>> TypeError: can't set attributes of built-in/extension
>>> type 'Dog.cmplx_int32'
>> 
>> Not quite, I'm setting a class attribute, not an attribute on an
>> instance.
>> 
> Quite. The problem is that extension types' attributes are determined by
> the layout of the object's slots and forever fixed in the C code that
> implements them: the slots can't be extended, so there's no way to add
> attributes. This is an efficiency feature: it would be *extremely* slow
> to look up the basic types' attributes using late-binding (it would also
> change the nature of the language somewhat, making it more like Ruby or
> Self).
> 
> So the reason you can't do what you want to is the same reason why you
> can't add attribute to the built-in types (which are, of course, clearly
> mentioned in the error message).
> 
>  >>> object.anyoldname = "You lose!"
> Traceback (most recent call last):
>    File "<stdin>", line 1, in <module>
> TypeError: can't set attributes of built-in/extension type 'object'
>  >>>
> 
> If you look in typeobject.c you'll find this error message occurs when
> the object's type isn't a PyHeapTypeObject (in other words, if it's one
> of the built-in or extension types).
> 
> regards
>   Steve

Thanks, but I'm a bit confused.  After reading in my "Python in a Nutshell",
I found that if after calling PyReady on my type object, if I use
PyDict_SetItemString (my_type_obj.tp_dict,)

That seems to work fine (which isn't exactly what it said in the Nutshell
book, but close).