preserve orig_nbformat when converting 3 to 4

preserves orig_nbformat = 2 in 2->3->4

IPython/nbformat/v4/convert.py

@@ -1,208 +1,209 b''
 """Code for converting notebooks to and from v3."""
 
 # Copyright (c) IPython Development Team.
 # Distributed under the terms of the Modified BSD License.
 
 import json
 
 from .nbbase import (
     nbformat, nbformat_minor,
     NotebookNode,
 )
 
 from IPython.nbformat import v3
 from IPython.utils.log import get_logger
 
 
 def upgrade(nb, from_version=3, from_minor=0):
     """Convert a notebook to v4.
 
     Parameters
     ----------
     nb : NotebookNode
         The Python representation of the notebook to convert.
     from_version : int
         The original version of the notebook to convert.
     from_minor : int
         The original minor version of the notebook to convert (only relevant for v >= 3).
     """
     from IPython.nbformat.current import validate, ValidationError
     if from_version == 3:
         # Validate the notebook before conversion
         try:
             validate(nb, version=from_version)
         except ValidationError as e:
             get_logger().error("Notebook JSON is not valid v%i: %s", from_version, e)
 
-        # Mark the original nbformat so consumers know it has been converted.
-        nb.pop('orig_nbformat', None)
-        nb.metadata.orig_nbformat = 3
+        # Mark the original nbformat so consumers know it has been converted
+        orig_nbformat = nb.pop('orig_nbformat', None)
+        nb.metadata.orig_nbformat = orig_nbformat or 3
+
         # Mark the new format
         nb.nbformat = nbformat
         nb.nbformat_minor = nbformat_minor
 
         # remove worksheet(s)
         nb['cells'] = cells = []
         # In the unlikely event of multiple worksheets,
         # they will be flattened
         for ws in nb.pop('worksheets', []):
             # upgrade each cell
             for cell in ws['cells']:
                 cells.append(upgrade_cell(cell))
         # upgrade metadata
         nb.metadata.pop('name', '')
         # Validate the converted notebook before returning it
         try:
             validate(nb, version=nbformat)
         except ValidationError as e:
             get_logger().error("Notebook JSON is not valid v%i: %s", nbformat, e)
         return nb
     elif from_version == 4:
         # nothing to do
         if from_minor != nbformat_minor:
             nb.metadata.orig_nbformat_minor = from_minor
         nb.nbformat_minor = nbformat_minor
 
         return nb
     else:
         raise ValueError('Cannot convert a notebook directly from v%s to v4.  ' \
                 'Try using the IPython.nbformat.convert module.' % from_version)
 
 def upgrade_cell(cell):
     """upgrade a cell from v3 to v4
 
     code cell:
         - remove language metadata
         - cell.input -> cell.source
         - update outputs
     """
     cell.setdefault('metadata', NotebookNode())
     if cell.cell_type == 'code':
         cell.pop('language', '')
         cell.metadata.collapsed = cell.pop('collapsed')
         cell.source = cell.pop('input')
         cell.setdefault('prompt_number', None)
         cell.outputs = upgrade_outputs(cell.outputs)
     elif cell.cell_type == 'html':
         # Technically, this exists. It will never happen in practice.
         cell.cell_type = 'markdown'
     return cell
 
 def downgrade_cell(cell):
     if cell.cell_type == 'code':
         cell.language = 'python'
         cell.input = cell.pop('source', '')
         cell.collapsed = cell.metadata.pop('collapsed', False)
         cell.outputs = downgrade_outputs(cell.outputs)
     return cell
 
 _mime_map = {
     "text" : "text/plain",
     "html" : "text/html",
     "svg" : "image/svg+xml",
     "png" : "image/png",
     "jpeg" : "image/jpeg",
     "latex" : "text/latex",
     "json" : "application/json",
     "javascript" : "application/javascript",
 };
 
 def to_mime_key(d):
     """convert dict with v3 aliases to plain mime-type keys"""
     for alias, mime in _mime_map.items():
         if alias in d:
             d[mime] = d.pop(alias)
     return d
 
 def from_mime_key(d):
     """convert dict with mime-type keys to v3 aliases"""
     for alias, mime in _mime_map.items():
         if mime in d:
             d[alias] = d.pop(mime)
     return d
 
 def upgrade_output(output):
     """upgrade a single code cell output from v3 to v4
 
     - pyout -> execute_result
     - pyerr -> error
     - mime-type keys
     - stream.stream -> stream.name
     """
     output.setdefault('metadata', NotebookNode())
     if output['output_type'] in {'pyout', 'display_data'}:
         if output['output_type'] == 'pyout':
             output['output_type'] = 'execute_result'
         to_mime_key(output)
         to_mime_key(output.metadata)
         if 'application/json' in output:
             output['application/json'] = json.loads(output['application/json'])
         # promote ascii bytes (from v2) to unicode
         for key in ('image/png', 'image/jpeg'):
             if key in output and isinstance(output[key], bytes):
                 output[key] = output[key].decode('ascii')
     elif output['output_type'] == 'pyerr':
         output['output_type'] = 'error'
     elif output['output_type'] == 'stream':
         output['name'] = output.pop('stream')
     return output
 
 def downgrade_output(output):
     """downgrade a single code cell output to v3 from v4
 
     - pyout <- execute_result
     - pyerr <- error
     - un-mime-type keys
     - stream.stream <- stream.name
     """
     if output['output_type'] == 'execute_result':
         output['output_type'] = 'pyout'
         if 'application/json' in output:
             output['application/json'] = json.dumps(output['application/json'])
         from_mime_key(output)
         from_mime_key(output.get('metadata', {}))
     elif output['output_type'] == 'error':
         output['output_type'] = 'pyerr'
     elif output['output_type'] == 'display_data':
         if 'application/json' in output:
             output['application/json'] = json.dumps(output['application/json'])
         from_mime_key(output)
         from_mime_key(output.get('metadata', {}))
     elif output['output_type'] == 'stream':
         output['stream'] = output.pop('name')
         output.pop('metadata')
     return output
 
 def upgrade_outputs(outputs):
     """upgrade outputs of a code cell from v3 to v4"""
     return [upgrade_output(op) for op in outputs]
 
 def downgrade_outputs(outputs):
     """downgrade outputs of a code cell to v3 from v4"""
     return [downgrade_output(op) for op in outputs]
 
 def downgrade(nb):
     """Convert a v4 notebook to v3.
 
     Parameters
     ----------
     nb : NotebookNode
         The Python representation of the notebook to convert.
     """
     from IPython.nbformat.current import validate
     # Validate the notebook before conversion
     validate(nb, version=nbformat)
 
     if nb.nbformat != 4:
         return nb
     nb.nbformat = v3.nbformat
     nb.nbformat_minor = v3.nbformat_minor
     cells = [ downgrade_cell(cell) for cell in nb.pop('cells') ]
     nb.worksheets = [v3.new_worksheet(cells=cells)]
     nb.metadata.setdefault('name', '')
     nb.metadata.pop('orig_nbformat', None)
     nb.metadata.pop('orig_nbformat_minor', None)
 
     # Validate the converted notebook before returning it
     validate(nb, version=v3.nbformat)
     return nb