Fix buggy RE “\parrot_example.py”, uncovered by Issue #27030

Lib/lib2to3/tests/test_refactor.py

@@ -8,6 +8,7 @@ import sys
 import os
 import codecs
 import operator
+import re
 import StringIO
 import tempfile
 import shutil
@@ -226,8 +227,8 @@ from __future__ import print_function"""
                                     actually_write=False)
         # Testing that it logged this message when write=False was passed is
         # sufficient to see that it did not bail early after "No changes".
-        message_regex = r"Not writing changes to .*%s%s" % (
-                os.sep, os.path.basename(test_file))
+        message_regex = r"Not writing changes to .*%s" % \
+                re.escape(os.sep + os.path.basename(test_file))
         for message in debug_messages:
             if "Not writing changes" in message:
                 self.assertRegexpMatches(message, message_regex)