+------------------------------+--------------------------------------+
| Value of *what* | Meaning of *arg* |
+==============================+======================================+
- | :const:`PyTrace_CALL` | Always *NULL*. |
+ | :const:`PyTrace_CALL` | Always :c:data:`Py_None`. |
+------------------------------+--------------------------------------+
| :const:`PyTrace_EXCEPTION` | Exception information as returned by |
| | :func:`sys.exc_info`. |
+------------------------------+--------------------------------------+
- | :const:`PyTrace_LINE` | Always *NULL*. |
+ | :const:`PyTrace_LINE` | Always :c:data:`Py_None`. |
+------------------------------+--------------------------------------+
| :const:`PyTrace_RETURN` | Value being returned to the caller, |
| | or *NULL* if caused by an exception. |