[capi-sig] What's up with PyTypeObject and functions?

[M.-A. Lemburg]

On 28.11.2012 04:01, Robert Steckroth wrote:
> Hey Gang, why is the below snippet for error checking not working? I wan't
> to be able to pass in different PyTypeObjects
> to the CHECK_TYPE function and check an object for that type.
> It works fine when I insert put &PyString_Type directly into
> the function like so -->
>   if ( ! PyObject_TypeCheck(s_obj, &PyString_type) )
> However, the CHECK_TYPE function will return -1 if I pass the PyTypeObject
> in, like at the bottom of this message.
> Why does PyObject_TypeCheck not work if PyTypeObject is first passed into a
> function?
> 
> 
> int CHECK_TYPE(PyObject *s_obj, PyTypeObject obj_type) {

You need *obj_type here, since you need the pointer to the object, not
the object itself.

>         if ( ! s_obj )
>              return 1;
> 
> if ( ! PyObject_TypeCheck(s_obj, &obj_type) ) {

This needs to be obj_type.

Your code will pass in the address of
the PyTypeObject on the stack, which will not match any of the
type objects in the Python type system.

>              PyErr_Format(PyExc_TypeError, "[ %s ] object needs to be of
> type [ %s ]\n\nUsage: %s", PyString_AsString(PyObject_Repr(s_obj)),
> obj_type.tp_name, obj_type.tp_doc );

This code leaks memory since the representation object is not freed.

>              return -1; }
> 
> return 1;
> 
> }
> 
> if ( !CHECK_TYPE(align, PyString_Type) ) return NULL;

This needs to the &PyString_Type

-- 
Marc-Andre Lemburg
eGenix.com

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