bpo-17799: Explain real behaviour of sys.settrace and sys.setprofile (#4056)

1 files changed, 6 insertions, 5 deletions

diff --git a/Doc/c-api/init.rst b/Doc/c-api/init.rst
index 4ee61e8..86faf47 100644
--- a/Doc/c-api/init.rst
+++ b/Doc/c-api/init.rst
@@ -1300,7 +1300,6 @@ Python-level trace functions in previous versions.
    | :const:`PyTrace_C_RETURN`    | Function object being called.        |
    +------------------------------+--------------------------------------+
 
-
 .. c:var:: int PyTrace_CALL
 
    The value of the *what* parameter to a :c:type:`Py_tracefunc` function when a new
@@ -1357,16 +1356,18 @@ Python-level trace functions in previous versions.
    function as its first parameter, and may be any Python object, or *NULL*.  If
    the profile function needs to maintain state, using a different value for *obj*
    for each thread provides a convenient and thread-safe place to store it.  The
-   profile function is called for all monitored events except the line-number
-   events.
+   profile function is called for all monitored events except :const:`PyTrace_LINE`
+   and :const:`PyTrace_EXCEPTION`.
 
 
 .. c:function:: void PyEval_SetTrace(Py_tracefunc func, PyObject *obj)
 
    Set the tracing function to *func*.  This is similar to
    :c:func:`PyEval_SetProfile`, except the tracing function does receive line-number
-   events.
-
+   events and does not receive any event related to C function objects being called. Any
+   trace function registered using :c:func:`PyEval_SetTrace` will not receive
+   :const:`PyTrace_C_CALL`, :const:`PyTrace_C_EXCEPTION` or :const:`PyTrace_C_RETURN`
+   as a value for the *what* parameter.
 
 .. _advanced-debugging: