Minor tweak to nbformat, still not passing test on Python 3.

IPython/nbformat/v2/nbjson.py

@@ -1,62 +1,62 b''
 """Read and write notebooks in JSON format.
 
 Authors:
 
 * Brian Granger
 """
 
 #-----------------------------------------------------------------------------
 #  Copyright (C) 2008-2011  The IPython Development Team
 #
 #  Distributed under the terms of the BSD License.  The full license is in
 #  the file COPYING, distributed as part of this software.
 #-----------------------------------------------------------------------------
 
 #-----------------------------------------------------------------------------
 # Imports
 #-----------------------------------------------------------------------------
 
 from base64 import encodestring
 from .nbbase import from_dict
 from .rwbase import NotebookReader, NotebookWriter, base64_decode
 import json
 
 #-----------------------------------------------------------------------------
 # Code
 #-----------------------------------------------------------------------------
 
 class BytesEncoder(json.JSONEncoder):
     def default(self, obj):
         if isinstance(obj, bytes):
-            return unicode(encodestring(bytes))
+            return encodestring(obj).decode('ascii')
         return json.JSONEncoder.default(self, obj)
 
 
 class JSONReader(NotebookReader):
 
     def reads(self, s, **kwargs):
         nb = json.loads(s, **kwargs)
         nb = self.to_notebook(nb, **kwargs)
         return nb
 
     def to_notebook(self, d, **kwargs):
         return base64_decode(from_dict(d))
 
 
 class JSONWriter(NotebookWriter):
 
     def writes(self, nb, **kwargs):
         kwargs['cls'] = BytesEncoder
         kwargs['indent'] = 4
         return json.dumps(nb, **kwargs)
 
 
 _reader = JSONReader()
 _writer = JSONWriter()
 
 reads = _reader.reads
 read = _reader.read
 to_notebook = _reader.to_notebook
 write = _writer.write
 writes = _writer.writes