Merge #17413: make sure settrace funcs get passed exception instances for 'value'.

Patch by Ingrid Cheung and Brendan McLoughlin.

Lib/test/test_sys_settrace.py

@@ -458,6 +458,29 @@ class RaisingTraceFuncTestCase(unittest.TestCase):
             self.fail("exception not propagated")
 
 
+    def test_exception_arguments(self):
+        def f():
+            x = 0
+            # this should raise an error
+            x.no_such_attr
+        def g(frame, event, arg):
+            if (event == 'exception'):
+                type, exception, trace = arg
+                self.assertIsInstance(exception, Exception)
+            return g
+
+        existing = sys.gettrace()
+        try:
+            sys.settrace(g)
+            try:
+                f()
+            except AttributeError:
+                # this is expected
+                pass
+        finally:
+            sys.settrace(existing)
+
+
 # 'Jump' tests: assigning to frame.f_lineno within a trace function
 # moves the execution position - it's how debuggers implement a Jump
 # command (aka. "Set next statement").

Misc/ACKS

@@ -211,6 +211,7 @@ David Chaum
 Nicolas Chauvat
 Jerry Chen
 Michael Chermside
+Ingrid Cheung
 Albert Chin-A-Young
 Adal Chiriliuc
 Matt Chisholm
@@ -802,6 +803,7 @@ Chris McDonough
 Greg McFarlane
 Alan McIntyre
 Michael McLay
+Brendan McLoughlin
 Mark Mc Mahon
 Gordon McMillan
 Andrew McNamara

Misc/NEWS

@@ -10,6 +10,10 @@ What's New in Python 3.4.0 Alpha 1?
 Core and Builtins
 -----------------
 
+- Issue #17413: sys.settrace callbacks were being passed a string instead of an
+  exception instance for the 'value' element of the arg tuple if the exception
+  originated from C code; now an exception instance is always provided.
+
 - Issue #17782: Fix undefined behaviour on platforms where
   ``struct timespec``'s "tv_nsec" member is not a C long.
 

Python/ceval.c

@@ -3793,6 +3793,7 @@ call_exc_trace(Py_tracefunc func, PyObject *self, PyFrameObject *f)
         value = Py_None;
         Py_INCREF(value);
     }
+    PyErr_NormalizeException(&type, &value, &traceback);
     arg = PyTuple_Pack(3, type, value, traceback);
     if (arg == NULL) {
         PyErr_Restore(type, value, traceback);