From 069560b1171eb6385121ff3b6331e8814a4e7454 Mon Sep 17 00:00:00 2001
From: Irit Katriel <iritkatriel@yahoo.com>
Date: Tue, 22 Dec 2020 19:53:09 +0000
Subject: [PATCH] bpo-34463: Make python tracebacks identical to C tracebacks
 for SyntaxErrors without a lineno (GH-23427)

---
 Lib/test/test_traceback.py                    | 25 +++++++++++++++++++
 Lib/traceback.py                              | 14 +++++++----
 .../2020-11-20-19-00-27.bpo-34463.aJcm56.rst  |  1 +
 3 files changed, 35 insertions(+), 5 deletions(-)
 create mode 100644 Misc/NEWS.d/next/Library/2020-11-20-19-00-27.bpo-34463.aJcm56.rst

diff --git a/Lib/test/test_traceback.py b/Lib/test/test_traceback.py
index 5df701caf0f..abb5762cd43 100644
--- a/Lib/test/test_traceback.py
+++ b/Lib/test/test_traceback.py
@@ -687,6 +687,31 @@ class BaseExceptionReportingTests:
         msg = self.get_report(e).splitlines()
         self.assertEqual(msg[-2], '               ^')
 
+    def test_syntax_error_no_lineno(self):
+        # See #34463.
+
+        # Without filename
+        e = SyntaxError('bad syntax')
+        msg = self.get_report(e).splitlines()
+        self.assertEqual(msg,
+            ['SyntaxError: bad syntax'])
+        e.lineno = 100
+        msg = self.get_report(e).splitlines()
+        self.assertEqual(msg,
+            ['  File "<string>", line 100', 'SyntaxError: bad syntax'])
+
+        # With filename
+        e = SyntaxError('bad syntax')
+        e.filename = 'myfile.py'
+
+        msg = self.get_report(e).splitlines()
+        self.assertEqual(msg,
+            ['SyntaxError: bad syntax (myfile.py)'])
+        e.lineno = 100
+        msg = self.get_report(e).splitlines()
+        self.assertEqual(msg,
+            ['  File "myfile.py", line 100', 'SyntaxError: bad syntax'])
+
     def test_message_none(self):
         # A message that looks like "None" should not be treated specially
         err = self.get_report(Exception(None))
diff --git a/Lib/traceback.py b/Lib/traceback.py
index 457d92511af..4e008bc0e08 100644
--- a/Lib/traceback.py
+++ b/Lib/traceback.py
@@ -525,7 +525,8 @@ class TracebackException:
         if exc_type and issubclass(exc_type, SyntaxError):
             # Handle SyntaxError's specially
             self.filename = exc_value.filename
-            self.lineno = str(exc_value.lineno)
+            lno = exc_value.lineno
+            self.lineno = str(lno) if lno is not None else None
             self.text = exc_value.text
             self.offset = exc_value.offset
             self.msg = exc_value.msg
@@ -584,9 +585,12 @@ class TracebackException:
     def _format_syntax_error(self, stype):
         """Format SyntaxError exceptions (internal helper)."""
         # Show exactly where the problem was found.
-        filename = self.filename or "<string>"
-        lineno = str(self.lineno) or '?'
-        yield '  File "{}", line {}\n'.format(filename, lineno)
+        filename_suffix = ''
+        if self.lineno is not None:
+            yield '  File "{}", line {}\n'.format(
+                self.filename or "<string>", self.lineno)
+        elif self.filename is not None:
+            filename_suffix = ' ({})'.format(self.filename)
 
         text = self.text
         if text is not None:
@@ -604,7 +608,7 @@ class TracebackException:
                 caretspace = ((c if c.isspace() else ' ') for c in ltext[:caret])
                 yield '    {}^\n'.format(''.join(caretspace))
         msg = self.msg or "<no detail available>"
-        yield "{}: {}\n".format(stype, msg)
+        yield "{}: {}{}\n".format(stype, msg, filename_suffix)
 
     def format(self, *, chain=True):
         """Format the exception.
diff --git a/Misc/NEWS.d/next/Library/2020-11-20-19-00-27.bpo-34463.aJcm56.rst b/Misc/NEWS.d/next/Library/2020-11-20-19-00-27.bpo-34463.aJcm56.rst
new file mode 100644
index 00000000000..df183548236
--- /dev/null
+++ b/Misc/NEWS.d/next/Library/2020-11-20-19-00-27.bpo-34463.aJcm56.rst
@@ -0,0 +1 @@
+Fixed discrepancy between :mod:`traceback` and the interpreter in formatting of SyntaxError with lineno not set (:mod:`traceback` was changed to match interpreter).