for prev_nb, nb, next_nb in prev_this_next(iter_notebooks()):

navbar = NAV_COMMENT

if prev_nb:

navbar += PREV_TEMPLATE.format(title=get_notebook_title(prev_nb),

url=prev_nb)

navbar += CONTENTS

if next_nb:

navbar += NEXT_TEMPLATE.format(title=get_notebook_title(next_nb),

url=next_nb)

navbar += COLAB_LINK.format(notebook_filename=os.path.basename(nb))

for nb_name, navbar in iter_navbars():

nb = nbformat.read(nb_name, as_version=4)

nb_file = os.path.basename(nb_name)

is_comment = lambda cell: cell.source.startswith(NAV_COMMENT)

if is_comment(nb.cells[1]):

print("- amending navbar for {0}".format(nb_file))

nb.cells[1].source = navbar

else:

print("- inserting navbar for {0}".format(nb_file))

nb.cells.insert(1, new_markdown_cell(source=navbar))

if is_comment(nb.cells[-1]):

nb.cells[-1].source = navbar

else:

nb.cells.append(new_markdown_cell(source=navbar))