gh-137716: TracebackException to handle messages with punctuation

Lib/test/test_traceback.py

@@ -3802,6 +3802,26 @@ def test_traceback_header(self):
         exc = traceback.TracebackException(Exception, Exception("haven"), None)
         self.assertEqual(list(exc.format()), ["Exception: haven\n"])
 
+    def test_exception_punctuation_handling_with_suggestions(self):
+        def raise_mssage(message, name):
+            try:
+                raise NameError(message, name=name)
+            except Exception as e:
+                return traceback.TracebackException.from_exception(e)._str
+
+        test_cases = [
+            ("Error.", "time", "Error. Did you forget to import 'time'?"),
+            ("Error?", "time", "Error? Did you forget to import 'time'?"),
+            ("Error!", "time", "Error! Did you forget to import 'time'?"),
+            ("Error", "time", "Error. Did you forget to import 'time'?"),
+            ("Error", "foo123", "Error"),
+        ]
+        for puctuation, name, expected in test_cases:
+            with self.subTest(puctuation=puctuation):
+                messsage = raise_mssage(puctuation, name)
+                self.assertEqual(messsage, expected)
+
+
     @requires_debug_ranges()
     def test_print(self):
         def f():

Lib/traceback.py

@@ -1081,50 +1081,33 @@ def __init__(self, exc_type, exc_value, exc_traceback, *, limit=None,
 
         self._is_syntax_error = False
         self._have_exc_type = exc_type is not None
-        if exc_type is not None:
+
+        if self._have_exc_type:
             self.exc_type_qualname = exc_type.__qualname__
             self.exc_type_module = exc_type.__module__
+            if issubclass(exc_type, SyntaxError):
+                # Handle SyntaxErrors specially
+                self.filename = exc_value.filename
+                lno = exc_value.lineno
+                self.lineno = str(lno) if lno is not None else None
+                end_lno = exc_value.end_lineno
+                self.end_lineno = str(end_lno) if end_lno is not None else None
+                self.text = exc_value.text
+                self.offset = exc_value.offset
+                self.end_offset = exc_value.end_offset
+                self.msg = exc_value.msg
+                self._is_syntax_error = True
+                self._exc_metadata = getattr(exc_value, "_metadata", None)
+            elif suggestion := _suggestion_message(exc_type, exc_value, exc_traceback):
+                if self._str.endswith(('.', '?', '!')):
+                    punctuation = ''
+                else:
+                    punctuation = '.'
+                self._str += f"{punctuation} {suggestion}"
         else:
             self.exc_type_qualname = None
             self.exc_type_module = None
 
-        if exc_type and issubclass(exc_type, SyntaxError):
-            # Handle SyntaxError's specially
-            self.filename = exc_value.filename
-            lno = exc_value.lineno
-            self.lineno = str(lno) if lno is not None else None
-            end_lno = exc_value.end_lineno
-            self.end_lineno = str(end_lno) if end_lno is not None else None
-            self.text = exc_value.text
-            self.offset = exc_value.offset
-            self.end_offset = exc_value.end_offset
-            self.msg = exc_value.msg
-            self._is_syntax_error = True
-            self._exc_metadata = getattr(exc_value, "_metadata", None)
-        elif exc_type and issubclass(exc_type, ImportError) and \
-                getattr(exc_value, "name_from", None) is not None:
-            wrong_name = getattr(exc_value, "name_from", None)
-            suggestion = _compute_suggestion_error(exc_value, exc_traceback, wrong_name)
-            if suggestion:
-                self._str += f". Did you mean: '{suggestion}'?"
-        elif exc_type and issubclass(exc_type, ModuleNotFoundError) and \
-                sys.flags.no_site and \
-                getattr(exc_value, "name", None) not in sys.stdlib_module_names:
-            self._str += (". Site initialization is disabled, did you forget to "
-                + "add the site-packages directory to sys.path?")
-        elif exc_type and issubclass(exc_type, (NameError, AttributeError)) and \
-                getattr(exc_value, "name", None) is not None:
-            wrong_name = getattr(exc_value, "name", None)
-            suggestion = _compute_suggestion_error(exc_value, exc_traceback, wrong_name)
-            if suggestion:
-                self._str += f". Did you mean: '{suggestion}'?"
-            if issubclass(exc_type, NameError):
-                wrong_name = getattr(exc_value, "name", None)
-                if wrong_name is not None and wrong_name in sys.stdlib_module_names:
-                    if suggestion:
-                        self._str += f" Or did you forget to import '{wrong_name}'?"
-                    else:
-                        self._str += f". Did you forget to import '{wrong_name}'?"
         if lookup_lines:
             self._load_lines()
         self.__suppress_context__ = \
@@ -1732,6 +1715,38 @@ def _compute_suggestion_error(exc_value, tb, wrong_name):
     return suggestion
 
 
+def _suggestion_message(exc_type, exc_value, exc_traceback):
+    if (
+        issubclass(exc_type, ModuleNotFoundError)
+        and sys.flags.no_site
+        and getattr(exc_value, "name", None) not in sys.stdlib_module_names
+    ):
+        return ("Site initialization is disabled, did you forget to "
+            "add the site-packages directory to sys.path?")
+    if issubclass(exc_type, (ImportError, NameError, AttributeError)):
+        if issubclass(exc_type, ImportError):
+            wrong_name = getattr(exc_value, "name_from", None)
+        else:
+            wrong_name = getattr(exc_value, "name", None)
+        if wrong_name:
+            other_name = _compute_suggestion_error(
+                exc_value, exc_traceback, wrong_name
+            )
+            maybe_stdlib_import = (
+                issubclass(exc_type, NameError)
+                and wrong_name in sys.stdlib_module_names
+            )
+            if not other_name:
+                if maybe_stdlib_import:
+                    return f"Did you forget to import '{wrong_name}'?"
+                return None
+            text = f"Did you mean: '{other_name}'?"
+            if maybe_stdlib_import:
+                return f"{text} Or did you forget to import '{wrong_name}'?"
+            return text
+    return None
+
+
 def _levenshtein_distance(a, b, max_cost):
     # A Python implementation of Python/suggestions.c:levenshtein_distance.
 

Misc/NEWS.d/next/Core_and_Builtins/2025-08-24-11-42-38.gh-issue-137716.7-Mtj-.rst

@@ -0,0 +1 @@
+Avoid double punctuation in :class:`~traceback.TracebackException` messages