Avoid matching '' or 'yn' when asking for 'y' or 'n' in interactive code

Lib/packaging/command/register.py

@@ -178,7 +178,7 @@ def send_metadata(self):
                         'will be faster.\n(the login will be stored in %s)',
                         get_pypirc_path())
                     choice = 'X'
-                    while choice.lower() not in 'yn':
+                    while choice.lower() not in ('y', 'n'):
                         choice = input('Save your login (y/N)?')
                         if not choice:
                             choice = 'n'

Lib/packaging/create.py

@@ -121,7 +121,7 @@ def ask_yn(question, default=None, helptext=None):
     question += ' (y/n)'
     while True:
         answer = ask(question, default, helptext, required=True)
-        if answer and answer[0].lower() in 'yn':
+        if answer and answer[0].lower() in ('y', 'n'):
             return answer[0].lower()
 
         print('\nERROR: You must select "Y" or "N".\n')