Use string.ascii_letters instead of string.letters (SF bug #226706).
diff --git a/Tools/scripts/fixheader.py b/Tools/scripts/fixheader.py
index 9b65a44..ba2e0c5 100755
--- a/Tools/scripts/fixheader.py
+++ b/Tools/scripts/fixheader.py
@@ -29,7 +29,7 @@
     sys.stderr.write('Processing %s ...\n' % file)
     magic = 'Py_'
     for c in file:
-        if c in string.letters + string.digits:
+        if c in string.ascii_letters + string.digits:
             magic = magic + string.upper(c)
         else: magic = magic + '_'
     sys.stdout = f