docs: def _generate_notebook_by_difficulty_body(notebook_object, dict_by_difficulty):
      """
      Internal function that is used for generation of the page where notebooks are organized by
      difficulty level.
  
      ----------
      Parameters
      ----------
      notebook_object : notebook object
          Object of "notebook" class where the body will be created.
  
      dict_by_difficulty : dict
          Global Dictionary that groups Notebooks names/files by difficulty level.
  
      """
  
      difficulty_keys = list(dict_by_difficulty.keys())
      difficulty_keys.sort()
      for difficulty in difficulty_keys:
          markdown_cell = STAR_TABLE_HEADER
          markdown_cell = _set_star_value(markdown_cell, int(difficulty))
          for notebook_file in dict_by_difficulty[str(difficulty)]:
              split_path = notebook_file.split("/")
              notebook_type = split_path[-2]
              notebook_name = split_path[-1].split("&")[0]
              notebook_title = split_path[-1].split("&")[1]
              markdown_cell += "\n\t<tr>\n\t\t<td width='20%' class='header_image_color_" + \
                               str(NOTEBOOK_KEYS[notebook_type]) + "'><img " \
                               "src='../../images/icons/" + notebook_type.title() +\
                               ".png' width='15%'>\n\t\t</td>"
              markdown_cell += "\n\t\t<td width='60%' class='center_cell open_cell_light'>" + \
                               notebook_title + "\n\t\t</td>"
              markdown_cell += "\n\t\t<td width='20%' class='center_cell'>\n\t\t\t<a href='" \
                               "../" + notebook_type.title() + "/" + notebook_name + \
                               "'><div class='file_icon'></div></a>\n\t\t</td>\n\t</tr>"
  
          markdown_cell += "</table>"
  
          # ==================== Insertion of HTML table in a new Notebook cell ======================
          notebook_object["cells"].append(nb.v4.new_markdown_cell(markdown_cell))