[3.8] bpo-34463: Make python tracebacks identical to C tracebacks for (#23899)

* [3.8] bpo-34463: Make python tracebacks identical to C tracebacks for
SyntaxErrors without a lineno (GH-23427)

(cherry picked from commit 069560b1171eb6385121ff3b6331e8814a4e7454)

Co-authored-by: Irit Katriel <iritkatriel@yahoo.com>

* 📜🤖 Added by blurb_it.

* added missing newline in test

Co-authored-by: blurb-it[bot] <43283697+blurb-it[bot]@users.noreply.github.com>

3 files changed, 34 insertions, 5 deletions

diff --git a/Lib/test/test_traceback.py b/Lib/test/test_traceback.py
index a5ba609..2ffb6fa 100644
--- a/Lib/test/test_traceback.py
+++ b/Lib/test/test_traceback.py
@@ -679,6 +679,30 @@ class BaseExceptionReportingTests:
         err = self.get_report(Exception(''))
         self.assertIn('Exception\n', err)
 
+    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'])
 
 class PyExcReportingTests(BaseExceptionReportingTests, unittest.TestCase):
     #
diff --git a/Lib/traceback.py b/Lib/traceback.py
index 19de84b..f76bdcf 100644
--- a/Lib/traceback.py
+++ b/Lib/traceback.py
@@ -515,7 +515,8 @@ 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
@@ -569,9 +570,12 @@ class TracebackException:
             return
 
         # It was a syntax error; 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)
 
         badline = self.text
         offset = self.offset
@@ -585,7 +589,7 @@ class TracebackException:
                 caretspace = ((c.isspace() and c or ' ') for c in caretspace)
                 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/2020-12-22-22-51-48.bpo-34463.TUD8V5.rst b/Misc/NEWS.d/next/Library/2020-12-22-22-51-48.bpo-34463.TUD8V5.rst
new file mode 100644
index 0000000..d045fb7
--- /dev/null
+++ b/Misc/NEWS.d/next/Library/2020-12-22-22-51-48.bpo-34463.TUD8V5.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).
\ No newline at end of file