[Python-Dev] Why is type_modified() in typeobject.c not a public function?

[Antoine Pitrou]

Stefan Behnel <stefan_ml <at> behnel.de> writes:
> BTW, I noticed that the code in typeobject.c uses "DECREF before set" two
> times, like this:
> 
> 		method_cache[h].version = type->tp_version_tag;
> 		method_cache[h].value = res;  /* borrowed */
> 		Py_INCREF(name);
> 		Py_DECREF(method_cache[h].name);
> 		method_cache[h].name = name;

Since this is so common, would it be useful to define a macro for the correct
construct?

Something like

#define Py_SETREF(var, obj) \
    { PyObject *tmp = (var); Py_INCREF(obj); \
      (var) = (obj); Py_XDECREF(tmp); }

Or, if we want to allow more optimizations, make two versions of it:

#define Py_SETREF(var, obj) \
    { PyObject *tmp = (var); Py_INCREF(obj); \
      (var) = (obj); Py_DECREF(tmp); }

#define Py_XSETREF(var, obj) \
    { PyObject *tmp = (var); Py_INCREF(obj); \
      (var) = (obj); Py_XDECREF(tmp); }

Regards

Antoine.