More work updating nbformat.

* Implemented conversion function (no-op for now).
* Other misc changes.

IPython/nbformat/current.py

@@ -28,14 +28,14 b' from IPython.nbformat import v1'
 from IPython.nbformat.v3 import (
     NotebookNode,
     new_code_cell, new_text_cell, new_notebook, new_output, new_worksheet,
-    parse_filename, new_metadata, new_author
+    parse_filename, new_metadata, new_author, new_heading_cell
 )
 
 #-----------------------------------------------------------------------------
 # Code
 #-----------------------------------------------------------------------------
 
-current_nbformat = 2
+current_nbformat = 3
 
 
 class NBFormatError(Exception):

IPython/nbformat/v3/__init__.py

@@ -19,7 +19,7 b' Authors:'
 from .nbbase import (
     NotebookNode,
     new_code_cell, new_text_cell, new_notebook, new_output, new_worksheet,
-    new_metadata, new_author
+    new_metadata, new_author, new_heading_cell
 )
 
 from .nbjson import reads as reads_json, writes as writes_json

IPython/nbformat/v3/convert.py

@@ -20,11 +20,13 b' from .nbbase import ('
     new_code_cell, new_text_cell, new_worksheet, new_notebook, new_output
 )
 
+from IPython.nbformat import v2
+
 #-----------------------------------------------------------------------------
 # Code
 #-----------------------------------------------------------------------------
 
-def convert_to_this_nbformat(nb, orig_version=1):
+def convert_to_this_nbformat(nb, orig_version=2):
     """Convert a notebook to the v2 format.
 
     Parameters
@@ -35,16 +37,12 b' def convert_to_this_nbformat(nb, orig_version=1):'
         The original version of the notebook to convert.
     """
     if orig_version == 1:
-        newnb = new_notebook()
-        ws = new_worksheet()
-        for cell in nb.cells:
-            if cell.cell_type == u'code':
-                newcell = new_code_cell(input=cell.get('code'),prompt_number=cell.get('prompt_number'))
-            elif cell.cell_type == u'text':
-                newcell = new_text_cell(u'markdown',source=cell.get('text'))
-            ws.cells.append(newcell)
-        newnb.worksheets.append(ws)
-        return newnb
+        nb = v2.convert_to_this_nbformat(nb)
+        orig_version = 2
+    if orig_version == 2:
+        return nb
+    elif orig_version == 3:
+        return nb
     else:
-        raise ValueError('Cannot convert a notebook from v%s to v2' % orig_version)
+        raise ValueError('Cannot convert a notebook from v%s to v3' % orig_version)
 

IPython/nbformat/v3/nbbase.py

@@ -146,7 +146,7 b' def new_worksheet(name=None, cells=None):'
 def new_notebook(metadata=None, worksheets=None):
     """Create a notebook by name, id and a list of worksheets."""
     nb = NotebookNode()
-    nb.nbformat = 2
+    nb.nbformat = 3
     if worksheets is None:
         nb.worksheets = []
     else: