Re: [PATCH v2 4/6] gdb: new setters and getters for __dict__, and attributes

[Matthieu Longo <matthieu.longo@arm.com>]

On 28/01/2026 18:00, Tom Tromey wrote:
>>>>>> "Matthieu" == Matthieu Longo <matthieu.longo@arm.com> writes:
> 
> Matthieu> GDB is currently using the Python unlimited API. Migrating the codebase
> Matthieu> to the Python limited API would have for benefit to make a GDB build
> Matthieu> artifacts compatible with older and newer versions of Python that they
> Matthieu> were built with.
> 
> Thanks again.
> 
> Matthieu> +  value = PyDict_GetItemWithError (dict.get (), attr);
> Matthieu> +  if (value != nullptr)
> Matthieu> +    return Py_NewRef (value);
> Matthieu> +
> Matthieu> +  /* PyDict_GetItemWithError() has a misleading name that lets one believe that
> Matthieu> +     the function sets PyExc_AttributeError when the key is not found, whereas
> Matthieu> +     it actually does not and only returns NULL.
> Matthieu> +     Not setting the exception for an unfound key causes the raising of another
> Matthieu> +     exception:
> Matthieu> +       <class 'SystemError'>: error return without exception set
> Matthieu> +     Hence this surprising manual setting of an exception to makes everything
> Matthieu> +     fit into place.  */
> Matthieu> +  PyErr_Format (PyExc_AttributeError,
> Matthieu> +		"'%s' object has no attribute '%s'",
> Matthieu> +		Py_TYPE (self)->tp_name,
> Matthieu> +		PyUnicode_AsUTF8AndSize (attr, nullptr));
> 
> 
> It seems to me that there should be an additional check between the call
> to PyDict_GetItemWithError and PyErr_Format, like:
> 
>      if (PyErr_Occurred () != nullptr)
>        return nullptr;
> 
> Since according to the PyDict_GetItemWithError docs, this function can
> return null with the error set.
> 
> With that change the comment could probably be shortened a bit since
> it's no longer surprising to have to set the exception.
> 
> Tom

I missed that. Thanks for noticing.

What about this ?

   value = PyDict_GetItemWithError (dict.get (), attr);
   if (value != nullptr)
     return Py_NewRef (value);

   /* If PyDict_GetItemWithError() returns NULL because an error occurred, it
      sets an exception.  Propagate it by returning NULL.  */
   if (PyErr_Occurred () != nullptr)
     return nullptr;

   /* If the key is not found, PyDict_GetItemWithError() returns NULL without
      setting an exception.  Failing to set one here would later result in:
        <class 'SystemError'>: error return without exception set
      Therefore, we must explicitly raise an AttributeError in this case.  */
   PyErr_Format (PyExc_AttributeError,
		"'%s' object has no attribute '%s'",
		Py_TYPE (self)->tp_name,
		PyUnicode_AsUTF8AndSize (attr, nullptr));
   return nullptr;

Matthieu