code: def construct_notebook_index(title, pthlst, pthidx):
      
  
      # Insert title text
      txt = '"""\n## %s\n"""\n\n"""' % title
      # Insert entry for each item in pthlst
      for pth in pthlst:
          # If pth refers to a .py file, replace .py with .ipynb, otherwise
          # assume it's a directory name and append '/index.ipynb'
          if pth[-3:] == '.py':
              link = os.path.splitext(pth)[0] + '.ipynb'
          else:
              link = os.path.join(pth, 'index.ipynb')
          txt += '- [%s](%s)\n' % (pthidx[pth], link)
      txt += '"""'
      return txt
docs: Construct a string containing a markdown format index for the list
      of paths in `pthlst`.  The title for the index is in `title`, and
      `pthidx` is a dict giving label text for each path.