docs: def code_cell(sourcecode):
      r"""
      Args:
          sourcecode (str):
  
      Returns:
          str: json formatted ipython notebook code cell
  
      CommandLine:
          python -m ibeis.templates.generate_notebook --exec-code_cell
  
      Example:
          >>> # DISABLE_DOCTEST
          >>> from ibeis.templates.generate_notebook import *  # NOQA
          >>> sourcecode = notebook_cells.timestamp_distribution[1]
          >>> sourcecode = notebook_cells.initialize[1]
          >>> result = code_cell(sourcecode)
          >>> print(result)
      """
      import utool as ut
      sourcecode = ut.remove_codeblock_syntax_sentinals(sourcecode)
      cell_header = ut.codeblock(
          '''
          {
           "cell_type": "code",
           "execution_count": null,
           "metadata": {
            "collapsed": true
           },
           "outputs": [],
           "source":
          ''')
      cell_footer = ut.codeblock(
          '''
          }
          ''')
      if sourcecode is None:
          source_line_repr = ' []\n'
      else:
          lines = sourcecode.split('\n')
          line_list = [line + '\n' if count < len(lines) else line
                       for count, line in enumerate(lines, start=1)]
          #repr_line_list = [repr_single_for_md(line) for line in line_list]
          repr_line_list = [repr_single_for_md(line) for line in line_list]
          source_line_repr = ut.indent(',\n'.join(repr_line_list), ' ' * 2)
          source_line_repr = ' [\n' + source_line_repr + '\n ]\n'
      return (cell_header + source_line_repr + cell_footer)