Issue #2173: fix build failure on OS X. device_encoding was returning an

empty string, causing an (invisible) LookupError on any attempt to write
to sys.stdout.

Misc/NEWS

@@ -12,6 +12,10 @@ What's New in Python 3.1 alpha 0
 Core and Builtins
 -----------------
 
+- Issue #2173: When getting device encoding, check that return value of
+  nl_langinfo is not the empty string.  This was causing silent build
+  failures on OS X.
+
 - Issue #4597: Fixed several opcodes that weren't always propagating
   exceptions.
 

Modules/posixmodule.c

@@ -6724,7 +6724,7 @@ device_encoding(PyObject *self, PyObject *args)
 #elif defined(CODESET)
 	{
 		char *codeset = nl_langinfo(CODESET);
-		if (codeset)
+		if (codeset != NULL && codeset[0] != 0)
 			return PyUnicode_FromString(codeset);
 	}
 #endif