Backport PR #2500: Add `encoding` attribute to `OutStream` class.

This means that `sys.stdout.encoding` returns something useful instead of raising an AttributeError.

Closes  #2220.

IPython/zmq/iostream.py

@@ -4,7 +4,7 b' from io import StringIO'
 
 from session import extract_header, Message
 
-from IPython.utils import io, text, encoding
+from IPython.utils import io, text
 
 #-----------------------------------------------------------------------------
 # Globals
@@ -22,6 +22,7 b' class OutStream(object):'
     topic=None
 
     def __init__(self, session, pub_socket, name):
+        self.encoding = 'UTF-8'
         self.session = session
         self.pub_socket = pub_socket
         self.name = name
@@ -69,8 +70,7 b' class OutStream(object):'
         else:
             # Make sure that we're handling unicode
             if not isinstance(string, unicode):
-                enc = encoding.DEFAULT_ENCODING
-                string = string.decode(enc, 'replace')
+                string = string.decode(self.encoding, 'replace')
             
             self._buffer.write(string)
             current_time = time.time()