How to use the httptools.is_same_url function in httptools

# TODO: better way to check if populate_metadata_from_tree did
            # anything useful?
            if paper.title in [None, ""]:
                log.debug("# TODO: parse metadata from html using plugins here")
            else:
                populated_metadata = True

        # can't try anything else if the url is still bad
        if paper.pdf_url in [None, ""]:
            continue

        # Normalize the two urls. The url from the metadata on the page
        # might be different from the url that was originally passed in,
        # even though both urls might still refer to the same resource.
        if is_same_url(url, paper.pdf_url):
            # pdf_url is same as original url, no pdf found yet. This
            # happens when the pdf url is correct, but the publisher is
            # returning html instead. And the html happens to reference the
            # url that was originally requested in the first place. Argh.
            continue

        log.debug("Switching activity to pdf_url {}".format(paper.pdf_url))

        # paper pdf is stored at a different url. Attempt to fetch that
        # url now. Only do this if pdf_url != url because otherwise
        # this will be an endless loop.
        for (url3, response2) in iterdownload(paper.pdf_url, paper=paper):
            if is_response_pdf(response2):
                log.debug("Got pdf on second-level page.")
                pdfcontent = remove_watermarks(response.content)
                paper.pdf = pdfcontent