Remove string.{letters,lowercase,uppercase}.
diff --git a/Lib/test/test_csv.py b/Lib/test/test_csv.py
index 21cc408..7ac52e3 100644
--- a/Lib/test/test_csv.py
+++ b/Lib/test/test_csv.py
@@ -645,7 +645,7 @@
 
     def test_char_write(self):
         import array, string
-        a = array.array('u', string.letters)
+        a = array.array('u', string.ascii_letters)
 
         with TemporaryFile("w+b") as fileobj:
             writer = csv.writer(fileobj, dialect="excel")