Use string.ascii_letters instead of string.letters (SF bug #226706).
diff --git a/Lib/Cookie.py b/Lib/Cookie.py
index dd116b7..3fc2ffc 100644
--- a/Lib/Cookie.py
+++ b/Lib/Cookie.py
@@ -249,7 +249,7 @@
 #       _LegalChars       is the list of chars which don't require "'s
 #       _Translator       hash-table for fast quoting
 #
-_LegalChars       = string.letters + string.digits + "!#$%&'*+-.^_`|~"
+_LegalChars       = string.ascii_letters + string.digits + "!#$%&'*+-.^_`|~"
 _Translator       = {
     '\000' : '\\000',  '\001' : '\\001',  '\002' : '\\002',
     '\003' : '\\003',  '\004' : '\\004',  '\005' : '\\005',