Try locale encoding if stdin encoding is ascii.

Starting the Qt console on Python 3, the kernel's stdin ends up with a .encoding of 'ascii' (whereas on Python 2 it is None). Since most platforms can handle a superset of ASCII, we may as well try locale.getpreferredencoding() in this case.

IPython/utils/text.py

@@ -47,7 +47,7 b' def getdefaultencoding():'
     and usually ASCII.
     """
     enc = sys.stdin.encoding
-    if not enc:
+    if not enc or enc=='ascii':
         try:
             # There are reports of getpreferredencoding raising errors
             # in some cases, which may well be fixed, but let's be conservative here.