old_contents: # Configuration file for jupyter-notebook.
  
  # Scrub output - pre save
  def scrub_output_pre_save(model, **kwargs):
      """scrub output before saving notebooks"""
      # only run on notebooks
      if model['type'] != 'notebook':
          return
      # only run on nbformat v4
      if model['content']['nbformat'] != 4:
          return
  
      for cell in model['content']['cells']:
          if cell['cell_type'] != 'code':
              continue
          cell['outputs'] = []
          cell['execution_count'] = None
  
  c.FileContentsManager.pre_save_hook = scrub_output_pre_save
  
  # Conver to python - post save
  import io
  import os
  from notebook.utils import to_api_path
  
  _script_exporter = None
  
  def script_post_save(model, os_path, contents_manager, **kwargs):
      """convert notebooks to Python script after save with nbconvert
  
      replaces `ipython notebook --script`
      """
      from nbconvert.exporters.script import ScriptExporter
  
      if model['type'] != 'notebook':
          return
  
      global _script_exporter
      if _script_exporter is None:
          _script_exporter = ScriptExporter(parent=contents_manager)
      log = contents_manager.log
  
      base, ext = os.path.splitext(os_path)
      py_fname = base + '.py'
      script, resources = _script_exporter.from_filename(os_path)
      script_fname = base + resources.get('output_extension', '.txt')
      log.info("Saving script /%s", to_api_path(script_fname, contents_manager.root_dir))
      with io.open(script_fname, 'w', encoding='utf-8') as f:
          f.write(script)
  c.FileContentsManager.post_save_hook = script_post_save
  
new_contents: # Configuration file for jupyter-notebook.
  
  # Config file hooks from: http://jupyter-notebook.readthedocs.io/en/latest/extending/savehooks.html
  
  # Scrub output - pre save
  def scrub_output_pre_save(model, **kwargs):
      """scrub output before saving notebooks"""
      # only run on notebooks
      if model['type'] != 'notebook':
          return
      # only run on nbformat v4
      if model['content']['nbformat'] != 4:
          return
  
      for cell in model['content']['cells']:
          if cell['cell_type'] != 'code':
              continue
          cell['outputs'] = []
          cell['execution_count'] = None
  
  c.FileContentsManager.pre_save_hook = scrub_output_pre_save
  
  # Conver to python - post save
  import io
  import os
  from notebook.utils import to_api_path
  
  _script_exporter = None
  
  def script_post_save(model, os_path, contents_manager, **kwargs):
      """convert notebooks to Python script after save with nbconvert
  
      replaces `ipython notebook --script`
      """
      from nbconvert.exporters.script import ScriptExporter
  
      if model['type'] != 'notebook':
          return
  
      global _script_exporter
      if _script_exporter is None:
          _script_exporter = ScriptExporter(parent=contents_manager)
      log = contents_manager.log
  
      base, ext = os.path.splitext(os_path)
      py_fname = base + '.py'
      script, resources = _script_exporter.from_filename(os_path)
      script_fname = base + resources.get('output_extension', '.txt')
      log.info("Saving script /%s", to_api_path(script_fname, contents_manager.root_dir))
      with io.open(script_fname, 'w', encoding='utf-8') as f:
          f.write(script)
  c.FileContentsManager.post_save_hook = script_post_save
  
subject: Add reference url.