bpo-45083: Include the exception class qualname when formatting an exception (pythonGH-28119)

Co-authored-by: Erlend Egeberg Aasland <erlend.aasland@innova.no>

Author: iritkatriel

Lib/test/test_sys.py

@@ -1070,6 +1070,20 @@ def __del__(self):
                     self.assertIn("del is broken", report)
                 self.assertTrue(report.endswith("\n"))
 
+    def test_original_unraisablehook_exception_qualname(self):
+        class A:
+            class B:
+                class X(Exception):
+                    pass
+
+        with test.support.captured_stderr() as stderr, \
+             test.support.swap_attr(sys, 'unraisablehook',
+                                    sys.__unraisablehook__):
+                 expected = self.write_unraisable_exc(
+                     A.B.X(), "msg", "obj");
+        report = stderr.getvalue()
+        testName = 'test_original_unraisablehook_exception_qualname'
+        self.assertIn(f"{testName}.<locals>.A.B.X", report)
 
     def test_original_unraisablehook_wrong_type(self):
         exc = ValueError(42)

Lib/test/test_traceback.py

@@ -1171,6 +1171,19 @@ def test_syntax_error_various_offsets(self):
                 exp = "\n".join(expected)
                 self.assertEqual(exp, err)
 
+    def test_format_exception_only_qualname(self):
+        class A:
+            class B:
+                class X(Exception):
+                    def __str__(self):
+                        return "I am X"
+                    pass
+        err = self.get_report(A.B.X())
+        str_value = 'I am X'
+        str_name = '.'.join([A.B.X.__module__, A.B.X.__qualname__])
+        exp = "%s: %s\n" % (str_name, str_value)
+        self.assertEqual(exp, err)
+
 
 class PyExcReportingTests(BaseExceptionReportingTests, unittest.TestCase):
     #

Misc/NEWS.d/next/Core and Builtins/2021-09-01-23-55-49.bpo-45083.cLi9G3.rst

@@ -0,0 +1,3 @@
+When the interpreter renders an exception, its name now has a complete qualname. Previously only the class name was concatenated to the module name, which sometimes resulted in an incorrect full name being displayed.
+
+(This issue impacted only the C code exception rendering, the :mod:`traceback` module was using qualname already).

Python/errors.c

@@ -1287,46 +1287,45 @@ write_unraisable_exc_file(PyThreadState *tstate, PyObject *exc_type,
     }
 
     assert(PyExceptionClass_Check(exc_type));
-    const char *className = PyExceptionClass_Name(exc_type);
-    if (className != NULL) {
-        const char *dot = strrchr(className, '.');
-        if (dot != NULL) {
-            className = dot+1;
-        }
-    }
 
-    PyObject *moduleName = _PyObject_GetAttrId(exc_type, &PyId___module__);
-    if (moduleName == NULL || !PyUnicode_Check(moduleName)) {
-        Py_XDECREF(moduleName);
+    PyObject *modulename = _PyObject_GetAttrId(exc_type, &PyId___module__);
+    if (modulename == NULL || !PyUnicode_Check(modulename)) {
+        Py_XDECREF(modulename);
         _PyErr_Clear(tstate);
         if (PyFile_WriteString("<unknown>", file) < 0) {
             return -1;
         }
     }
     else {
-        if (!_PyUnicode_EqualToASCIIId(moduleName, &PyId_builtins)) {
-            if (PyFile_WriteObject(moduleName, file, Py_PRINT_RAW) < 0) {
-                Py_DECREF(moduleName);
+        if (!_PyUnicode_EqualToASCIIId(modulename, &PyId_builtins)) {
+            if (PyFile_WriteObject(modulename, file, Py_PRINT_RAW) < 0) {
+                Py_DECREF(modulename);
                 return -1;
             }
-            Py_DECREF(moduleName);
+            Py_DECREF(modulename);
             if (PyFile_WriteString(".", file) < 0) {
                 return -1;
             }
         }
         else {
-            Py_DECREF(moduleName);
+            Py_DECREF(modulename);
         }
     }
-    if (className == NULL) {
+
+    PyObject *qualname = PyType_GetQualName((PyTypeObject *)exc_type);
+    if (qualname == NULL || !PyUnicode_Check(qualname)) {
+        Py_XDECREF(qualname);
+        _PyErr_Clear(tstate);
         if (PyFile_WriteString("<unknown>", file) < 0) {
             return -1;
         }
     }
     else {
-        if (PyFile_WriteString(className, file) < 0) {
+        if (PyFile_WriteObject(qualname, file, Py_PRINT_RAW) < 0) {
+            Py_DECREF(qualname);
             return -1;
         }
+        Py_DECREF(qualname);
     }
 
     if (exc_value && exc_value != Py_None) {

Python/pythonrun.c

@@ -961,36 +961,37 @@ print_exception(PyObject *f, PyObject *value)
         /* Don't do anything else */
     }
     else {
-        PyObject* moduleName;
-        const char *className;
+        PyObject* modulename;
+
         _Py_IDENTIFIER(__module__);
         assert(PyExceptionClass_Check(type));
-        className = PyExceptionClass_Name(type);
-        if (className != NULL) {
-            const char *dot = strrchr(className, '.');
-            if (dot != NULL)
-                className = dot+1;
-        }
 
-        moduleName = _PyObject_GetAttrId(type, &PyId___module__);
-        if (moduleName == NULL || !PyUnicode_Check(moduleName))
+        modulename = _PyObject_GetAttrId(type, &PyId___module__);
+        if (modulename == NULL || !PyUnicode_Check(modulename))
         {
-            Py_XDECREF(moduleName);
+            Py_XDECREF(modulename);
+            PyErr_Clear();
             err = PyFile_WriteString("<unknown>", f);
         }
         else {
-            if (!_PyUnicode_EqualToASCIIId(moduleName, &PyId_builtins))
+            if (!_PyUnicode_EqualToASCIIId(modulename, &PyId_builtins))
             {
-                err = PyFile_WriteObject(moduleName, f, Py_PRINT_RAW);
+                err = PyFile_WriteObject(modulename, f, Py_PRINT_RAW);
                 err += PyFile_WriteString(".", f);
             }
-            Py_DECREF(moduleName);
+            Py_DECREF(modulename);
         }
         if (err == 0) {
-            if (className == NULL)
-                      err = PyFile_WriteString("<unknown>", f);
-            else
-                      err = PyFile_WriteString(className, f);
+            PyObject* qualname = PyType_GetQualName((PyTypeObject *)type);
+            if (qualname == NULL || !PyUnicode_Check(qualname)) {
+                Py_XDECREF(qualname);
+                PyErr_Clear();
+                err = PyFile_WriteString("<unknown>", f);
+            }
+            else {
+                err = PyFile_WriteObject(qualname, f, Py_PRINT_RAW);
+                Py_DECREF(qualname);
+            }
         }
     }
     if (err == 0 && (value != Py_None)) {