Default to ASCII as the locale.getpreferredencoding, if the POSIX

system doesn't support CODESET and LANG isn't set or doesn't
allow deduction of an encoding.

Lib/locale.py

@@ -505,7 +505,11 @@ def getpreferredencoding(do_setlocale = True):
         def getpreferredencoding(do_setlocale = True):
             """Return the charset that the user is likely using,
             by looking at environment variables."""
-            return getdefaultlocale()[1]
+            res = getdefaultlocale()[1]
+            if res is None:
+                # LANG not set, default conservatively to ASCII
+                res = 'ascii'
+            return res
     else:
         def getpreferredencoding(do_setlocale = True):
             """Return the charset that the user is likely using,

Misc/NEWS

@@ -14,6 +14,13 @@ Extension Modules
 
 - Use wchar_t functions in _locale module.
 
+Library
+-------
+
+- Default to ASCII as the locale.getpreferredencoding, if the POSIX
+  system doesn't support CODESET and LANG isn't set or doesn't
+  allow deduction of an encoding.
+
 
 What's New in Python 3.0a3?
 ===========================