gh-138978: Fully qualified name for abc classes exception. by skv0zsneg · Pull Request #156683 · python/cpython

skv0zsneg · 2026-08-30T20:42:16Z

Issue: Improve UX by using fully-qualified name in some TypeError #138978

skv0zsneg · 2026-08-30T20:50:13Z


    def check_program_exitcode(self, *args, check_stderr=True, **kwargs):
        out, err = self.run_embedded_interpreter(*args, **kwargs)
-        self.assertEqual(out.rstrip(), 'ok! Py_RunMain() returned 123')


After adding changes to tests and typeobjec.c the strange error appear

AssertionError: 'Cmd click to launch VS Code Native REPL\nok! Py_RunMain() returned 123' != 'ok! Py_RunMain() returned 123' - Cmd click to launch VS Code Native REPL ok! Py_RunMain() returned 123

So, I changed it for checking exactly "ok!..." string.

Could you check if it happens from CLI? My hunch is that it's VS Code artifact

Wow, yes. From CLI test is not falling.

I do not clearly understand what this test (and others in Lib/test/test_embed.py) checking. Integrations with IDE's?

maurycy

I suspect that the C part can be a bit smaller, using %N

cpython/Objects/unicodeobject.c

Lines 3019 to 3049 in aad4288

    
           case 'N': 
        
           { 
        
               PyObject *type_raw = va_arg(*vargs, PyObject *); 
        
               assert(type_raw != NULL); 
        
               if (!PyType_Check(type_raw)) { 
        
                   PyErr_SetString(PyExc_TypeError, "%N argument must be a type"); 
        
                   return NULL; 
        
               } 
        
               PyTypeObject *type = (PyTypeObject*)type_raw; 
        
               PyObject *type_name; 
        
               if (flags & F_ALT) { 
        
                   type_name = _PyType_GetFullyQualifiedName(type, ':'); 
        
               } 
        
               else { 
        
                   type_name = PyType_GetFullyQualifiedName(type); 
        
               } 
        
               if (!type_name) { 
        
                   return NULL; 
        
               } 
        
               if (unicode_fromformat_write_str(writer, type_name, 
        
                                                width, precision, flags) == -1) { 
        
                   Py_DECREF(type_name); 
        
                   return NULL; 
        
               } 
        
               Py_DECREF(type_name); 
        
               break; 
        
           } 
        
           default:

maurycy · 2026-08-31T13:08:11Z

            return NULL;
        }

+        PyObject *type_name = _PyType_GetFullyQualifiedName(type, '.');


Could you check if PyErr_Format already does this via %N?

Yep! It works, and all test (locally) passes! Amazing, thank you!

I wonder do docs have information about this cpython special string formats?

Yup: https://docs.python.org/3/c-api/unicode.html#c.PyUnicode_FromFormat

maurycy · 2026-08-31T13:11:37Z

@@ -0,0 +1 @@
+Add fully qualified name for abc class initialization exception.


Maybe it should describe the user-visible change more, eg:

Suggested change

Add fully qualified name for abc class initialization exception.

The :exc:`TypeError` raised when instantiating an abstract class with unimplemented abstract methods now includes the fully qualified name of the class.

I love your version, thanks! I rewrite it like this

maurycy · 2026-08-31T21:03:16Z

+                with self.assertRaises(TypeError) as cm:
+                    self.MyAbstractClass()
+
+                print(str(cm.exception))


Left-over from debugging?

Suggested change

print(str(cm.exception))

Oh, how I missed this... Will remove

maurycy · 2026-08-31T21:09:28Z

-                                                                     abc.get_cache_token)
+    class TestAbstractClassErrorMessage(unittest.TestCase):
+
+        class MyAbstractClass(abc.ABC):


I think that abc_ABCMeta should be used here. My understanding is that test_factory creates a class twice - for C and Py variants - and hard-coded abc.ABC prevents the magic from happening :-)

maurycy · 2026-08-31T21:11:03Z

@@ -0,0 +1 @@
+The :exc:`TypeError` raised when instantiating an abstract class with unimplemented abstract methods now includes the fully qualified name of the class.


Nit:

Suggested change

The :exc:`TypeError` raised when instantiating an abstract class with unimplemented abstract methods now includes the fully qualified name of the class.

The :exc:`TypeError` raised when instantiating an abstract class with

unimplemented abstract methods now includes the fully qualified name of the

class.

I'm sorry for this one, was typing from my phone. Typically we wrap around ~79 chars, as per https://devguide.python.org/documentation/markup/#use-of-whitespace

No problem! Will know, thanks again!

skv0zsneg added 3 commits August 30, 2026 23:27

Add full qualified name for abc class execption.

a088e53

Fix and add more tests.

ef073f9

Fix tests.

6a55e29

skv0zsneg requested review from ericvsmith and markshannon as code owners August 30, 2026 20:42

bedevere-app Bot added the awaiting review label Aug 30, 2026

bedevere-app Bot mentioned this pull request Aug 30, 2026

Improve UX by using fully-qualified name in some TypeError #138978

Open

📜🤖 Added by blurb_it.

2d43e72

skv0zsneg commented Aug 30, 2026

View reviewed changes

maurycy reviewed Aug 31, 2026

View reviewed changes

skv0zsneg added 3 commits August 31, 2026 23:34

Improve news message.

c0e6f78

Improve detailed text message.

1ad5630

Revert embed test fix.

d404787

maurycy reviewed Aug 31, 2026

View reviewed changes

skv0zsneg added 5 commits September 1, 2026 01:11

Remove debug print.

cf11484

Fix class definition.

fdb4b6b

FIx news format.

09ad373

Merge remote-tracking branch 'upstream/main' into fix-issue-138978

ca04150

Add new line.

cd64d2c

	case 'N':
	{
	PyObject type_raw = va_arg(vargs, PyObject *);
	assert(type_raw != NULL);

	if (!PyType_Check(type_raw)) {
	PyErr_SetString(PyExc_TypeError, "%N argument must be a type");
	return NULL;
	}
	PyTypeObject type = (PyTypeObject)type_raw;

	PyObject *type_name;
	if (flags & F_ALT) {
	type_name = _PyType_GetFullyQualifiedName(type, ':');
	}
	else {
	type_name = PyType_GetFullyQualifiedName(type);
	}
	if (!type_name) {
	return NULL;
	}
	if (unicode_fromformat_write_str(writer, type_name,
	width, precision, flags) == -1) {
	Py_DECREF(type_name);
	return NULL;
	}
	Py_DECREF(type_name);
	break;
	}

	default:

		@@ -0,0 +1 @@
		Add fully qualified name for abc class initialization exception.

	Add fully qualified name for abc class initialization exception.
	The :exc:`TypeError` raised when instantiating an abstract class with unimplemented abstract methods now includes the fully qualified name of the class.

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skv0zsneg commented Aug 30, 2026 •

edited by bedevere-app Bot

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skv0zsneg Aug 30, 2026 •

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