How to use the pypandoc.pandoc_download.download_pandoc function in pypandoc

def ensure_pandoc_installed(url=None, targetfolder=None, version="latest", quiet=False, delete_installer=False):
    """Try to install pandoc if it isn't installed.

    Parameters are passed to download_pandoc()

    :raises OSError: if pandoc cannot be installed
    """
    try:
        # Perform the test quietly if asked
        _ensure_pandoc_path(quiet=quiet)

    except OSError:
        download_pandoc(url=url, targetfolder=targetfolder, version=version, quiet=quiet, delete_installer=delete_installer)

        # Show errors in case of secondary failure
        _ensure_pandoc_path(quiet=False)

# First, try to use convert_file, assuming Pandoc is already installed.
        # If that fails, try to download & install it, and then try to convert
        # again.
        # noinspection PyBroadException
        try:
            # pandoc, you rock...
            rst_content = convert_file(md_path, 'rst')
            with open(rst_path, 'w') as rst_file:
                for line in rst_content.splitlines(keepends=False):
                    rst_file.write(line + '\n')
        except Exception:
            try:
                # noinspection PyUnresolvedReferences,PyPackageRequirements
                from pypandoc.pandoc_download import download_pandoc

                download_pandoc()
            except FileNotFoundError:
                warnings.warn("Unable to download & install pandoc. Unable to generate README.rst.")
            else:
                # pandoc, you rock...
                rst_content = convert_file(md_path, 'rst')
                with open(rst_path, 'w') as rst_file:
                    for line in rst_content.splitlines(keepends=False):
                        rst_file.write(line + '\n')

    if os.path.isfile(rst_path):
        with open(rst_path) as rst_file:
            return rst_file.read()
    else:
        # It will be messy, but it's better than nothing...
        with open(md_path) as md_file:
            return md_file.read()

def run(self):
        from pypandoc.pandoc_download import download_pandoc
        targetfolder = os.path.join(os.path.dirname(os.path.realpath(__file__)), "pypandoc", "files")
        download_pandoc(targetfolder=targetfolder)