How to use the nbconvert.export function in nbconvert

def run_test(project, zone, cluster, new_values):  # pylint: disable=too-many-locals
    # TODO(jeremy@lewi.us): Need to configure the notebook and test to build
    # using GCB.
    dirname = os.path.dirname(__file__)
    if not dirname:
      logging.info("__file__ doesn't apper to be absolute path.")
      dirname = os.getcwd()
    notebook_path = os.path.join(dirname, "TF on GKE.ipynb")
    logging.info("Reading notebook %s", notebook_path)
    if not os.path.exists(notebook_path):
      raise ValueError("%s does not exist" % notebook_path)

    with open(notebook_path) as hf:
      node = nbformat.read(hf, nbformat.NO_CONVERT)
    exporter = nbconvert.PythonExporter()
    raw, _ = nbconvert.export(exporter, node)

    credentials = GoogleCredentials.get_application_default()
    gke = discovery.build("container", "v1", credentials=credentials)

    lines = raw.splitlines()

    modified = replace_vars(lines, new_values)

    modified = strip_appendix(modified)

    modified = strip_unexecutable(modified)

    with tempfile.NamedTemporaryFile(suffix="notebook.py", prefix="tmpGke",
                                     mode="w", delete=False) as hf:
      code_path = hf.name
      hf.write("\n".join(modified))

After doing this it will take a python file that contains assert statements
    and will throw a status code of 2 if there are failures. Will also print
    the prefixed error message.
    :param ipynbfile: the notebook file
    :param pyfile: the python file
    :param verbose: turn on verbose mode, will print the code in both files
    :param prefix: optional prefix to add to the error message
    """
    if os.path.splitext(ipynbfile)[1] != '.ipynb':
        raise ValueError(".ipynb file needs to have .ipynb extension")
    if os.path.splitext(pyfile)[1] != '.py':
        raise ValueError(".py file needs to have .py extension")

    with open(ipynbfile, 'r') as readfile:
        notebook = nbformat.read(readfile, as_version=nbformat.NO_CONVERT)
    output, metadata = nbconvert.export(nbconvert.PythonExporter, notebook)
    if verbose:
        for i, cell in enumerate(output.split("#")):
            code = "#" + cell
            click.echo(click.style(f'showing block {i}', fg='blue'))
            for line in code.split("\n"):
                if line != "\n":
                    print("  " + line)
            try:
                exec(code)
            except:
                click.echo(click.style(f"Error in codeblock!", fg='red'))
                traceback.print_exc()
                click.echo(click.style(f"{prefix}notebook contains error, could not even pass it to py-file.", fg='red'))
                sys.exit(2)

    click.echo(click.style(f"Notebook {ipynbfile} has been parsed.", fg='blue'))

""" This script is called by sphinxdoc to convert all Jupyter notebooks in the
Examples folder to ReStructured Text files and stores them in the documentation
folder.

Author: R.A. Collenteur 2016
"""

import nbconvert
from nbconvert import RSTExporter
import glob
import io
import os

notebooks = glob.iglob('../examples/notebooks/*.ipynb')
for nb in notebooks:
    (x,resources) = nbconvert.export(RSTExporter, nb)
    name = os.path.basename(nb)[:-6]
    pathname = '../doc/examples/{0}'.format(name)
    if not os.path.isdir(pathname):
        os.makedirs(pathname)
    fname = os.path.join(pathname,'{}.rst'.format(name))
    with io.open(fname, 'w', encoding='utf-8') as f:
        f.write(x[:])
    for output in resources['outputs'].keys():
        fname = os.path.join(pathname,output)
        with io.open(fname, 'wb') as f:
            f.write(resources['outputs'][output])

print("example notebooks successfully converted to .rst files")

assert os.path.isfile(nam_fp), f'{nam_fp} does not exist'
        mp = Model(nam_fp)
        nb = mp.script_model2nb(use_yapf=False)

        buff = io.BytesIO()
        zip_out = zipfile.ZipFile(buff, 'w')

        ipynb_buff = io.StringIO(nbformat.writes(nb))
        zip_out.writestr('test.ipynb', ipynb_buff.getvalue())

        for out_formats_item, out_formats_ext_item in zip(
                out_formats, out_formats_ext):
            ipynb_buff.seek(0)
            zip_out.writestr('test.' + out_formats_ext_item,
                             nbconvert.export(
                                 nbconvert.get_exporter(out_formats_item),
                                 ipynb_buff)[0])

        ipynb_buff.close()
        zip_out.close()
        print('\nContent of the zipfile:')
        zip_out.printdir()

    return buff

p_list_order = list(mp.packages.keys())
    toc = [
        '* [' + i + '](#' + i.replace('.', '') + ')\n' for i in p_list_order
    ]
    toc = ''.join(toc)

    with open('wiki_default_parameters.md', 'w') as f:
        f.write(toc)
        f.write(s)

    ipynb_buff.close()

    # without discription
    nb = mp.script_model2nb(print_descr=False, use_yapf=False)
    ipynb_buff = io.StringIO(nbformat.writes(nb))
    s = nbconvert.export(nbconvert.get_exporter('markdown'), ipynb_buff)[0]

    s = s.replace('\n\n```', '\n\n```python')

    p_list_order = list(mp.packages.keys())
    toc = [
        '* [' + i + '](#' + i.replace('.', '') + ')\n' for i in p_list_order
    ]
    toc = ''.join(toc)

    with open('wiki_default_parameters_without_description.md', 'w') as f:
        f.write(toc)
        f.write(s)

    ipynb_buff.close()

except OSError as e: