Issue #17825: Cursor ^ is correctly positioned for SyntaxError and IndentationError.

Lib/test/test_traceback.py

@@ -35,6 +35,9 @@ class TracebackCases(unittest.TestCase):
     def syntax_error_bad_indentation(self):
         compile("def spam():\n  print 1\n print 2", "?", "exec")
 
+    def syntax_error_bad_indentation2(self):
+        compile(" print(2)", "?", "exec")
+
     def test_caret(self):
         err = self.get_exception_format(self.syntax_error_with_caret,
                                         SyntaxError)
@@ -111,6 +114,13 @@ def test():
                 os.unlink(os.path.join(testdir, f))
             os.rmdir(testdir)
 
+        err = self.get_exception_format(self.syntax_error_bad_indentation2,
+                                        IndentationError)
+        self.assertEqual(len(err), 4)
+        self.assertEqual(err[1].strip(), "print(2)")
+        self.assertIn("^", err[2])
+        self.assertEqual(err[1].find("p"), err[2].find("^"))
+
     def test_base_exception(self):
         # Test that exceptions derived from BaseException are formatted right
         e = KeyboardInterrupt()

Lib/traceback.py

@@ -189,11 +189,12 @@ def format_exception_only(etype, value):
         if badline is not None:
             lines.append('    %s\n' % badline.strip())
             if offset is not None:
-                caretspace = badline.rstrip('\n')[:offset].lstrip()
+                caretspace = badline.rstrip('\n')
+                offset = min(len(caretspace), offset) - 1
+                caretspace = caretspace[:offset].lstrip()
                 # non-space whitespace (likes tabs) must be kept for alignment
                 caretspace = ((c.isspace() and c or ' ') for c in caretspace)
-                # only three spaces to account for offset1 == pos 0
-                lines.append('   %s^\n' % ''.join(caretspace))
+                lines.append('    %s^\n' % ''.join(caretspace))
         value = msg
 
     lines.append(_format_final_exc_line(stype, value))

Misc/NEWS

@@ -9,6 +9,9 @@ What's New in Python 2.7.7?
 Core and Builtins
 -----------------
 
+- Issue #17825: Cursor "^" is correctly positioned for SyntaxError and
+  IndentationError.
+
 - Issue #19081: When a zipimport .zip file in sys.path being imported from
   is modified during the lifetime of the Python process after zipimport has
   already cached the zip's table of contents we detect this and recover