How to use the telegraph.upload.FilesOpener function in telegraph

def upload_file(f):
    """ Upload file to Telegra.ph's servers. Returns a list of links.
        Allowed only .jpg, .jpeg, .png, .gif and .mp4 files.

    :param f: filename or file-like object.
    :type f: file, str or list
    """
    with FilesOpener(f) as files:
        response = requests.post(
            'https://telegra.ph/upload',
            files=files
        ).json()

    if isinstance(response, list):
        error = response[0].get('error')
    else:
        error = response.get('error')

    if error:
        raise TelegraphException(error)

    return [i['src'] for i in response]