How to use the pip._vendor.six.moves.urllib.parse.urljoin function in pip

url = link.url.split('#', 1)[0]

    # Check for VCS schemes that do not support lookup as web pages.
    vcs_scheme = _match_vcs_scheme(url)
    if vcs_scheme:
        logger.debug('Cannot look at %s URL %s', vcs_scheme, link)
        return None

    # Tack index.html onto file:// URLs that point to directories
    scheme, _, path, _, _, _ = urllib_parse.urlparse(url)
    if (scheme == 'file' and os.path.isdir(urllib_request.url2pathname(path))):
        # add trailing slash if not present so urljoin doesn't trim
        # final segment
        if not url.endswith('/'):
            url += '/'
        url = urllib_parse.urljoin(url, 'index.html')
        logger.debug(' file: URL is directory, getting %s', url)

    try:
        resp = _get_html_response(url, session=session)
    except _NotHTTP:
        logger.debug(
            'Skipping page %s because it looks like an archive, and cannot '
            'be checked by HEAD.', link,
        )
    except _NotHTML as exc:
        logger.debug(
            'Skipping page %s because the %s request got Content-Type: %s',
            link, exc.request_desc, exc.content_type,
        )
    except HTTPError as exc:
        _handle_get_page_fail(link, exc)

url = link.url.split('#', 1)[0]

    # Check for VCS schemes that do not support lookup as web pages.
    vcs_scheme = _match_vcs_scheme(url)
    if vcs_scheme:
        logger.debug('Cannot look at %s URL %s', vcs_scheme, link)
        return None

    # Tack index.html onto file:// URLs that point to directories
    scheme, _, path, _, _, _ = urllib_parse.urlparse(url)
    if (scheme == 'file' and os.path.isdir(urllib_request.url2pathname(path))):
        # add trailing slash if not present so urljoin doesn't trim
        # final segment
        if not url.endswith('/'):
            url += '/'
        url = urllib_parse.urljoin(url, 'index.html')
        logger.debug(' file: URL is directory, getting %s', url)

    try:
        resp = _get_html_response(url, session=session)
    except _NotHTTP:
        logger.debug(
            'Skipping page %s because it looks like an archive, and cannot '
            'be checked by HEAD.', link,
        )
    except _NotHTML as exc:
        logger.debug(
            'Skipping page %s because the %s request got Content-Type: %s',
            link, exc.request_desc, exc.content_type,
        )
    except HTTPError as exc:
        _handle_get_page_fail(link, exc)

content_type,
                    )
                    return

        logger.debug('Getting page %s', url)

        # Tack index.html onto file:// URLs that point to directories
        (scheme, netloc, path, params, query, fragment) = \
            urllib_parse.urlparse(url)
        if (scheme == 'file' and
                os.path.isdir(urllib_request.url2pathname(path))):
            # add trailing slash if not present so urljoin doesn't trim
            # final segment
            if not url.endswith('/'):
                url += '/'
            url = urllib_parse.urljoin(url, 'index.html')
            logger.debug(' file: URL is directory, getting %s', url)

        resp = session.get(
            url,
            headers={
                "Accept": "text/html",
                # We don't want to blindly returned cached data for
                # /simple/, because authors generally expecting that
                # twine upload && pip install will function, but if
                # they've done a pip install in the last ~10 minutes
                # it won't. Thus by setting this to zero we will not
                # blindly use any cached data, however the benefit of
                # using max-age=0 instead of no-cache, is that we will
                # still support conditional requests, so we will still
                # minimize traffic sent in cases where the page hasn't
                # changed at all, we will just always incur the round

def links(self):
        """Yields all links in the page"""
        for anchor in self.parsed.findall(".//a"):
            if anchor.get("href"):
                href = anchor.get("href")
                url = self.clean_link(
                    urllib_parse.urljoin(self.base_url, href)
                )

                # Determine if this link is internal. If that distinction
                #   doesn't make sense in this context, then we don't make
                #   any distinction.
                internal = None
                if self.api_version and self.api_version >= 2:
                    # Only api_versions >= 2 have a distinction between
                    #   external and internal links
                    internal = bool(
                        anchor.get("rel")
                        and "internal" in anchor.get("rel").split()
                    )

                yield Link(url, self, internal=internal)

def url_to_path(self, path):
        return urllib_parse.urljoin(self.url, path)

def iter_links(self):
        # type: () -> Iterable[Link]
        """Yields all links in the page"""
        document = html5lib.parse(
            self.content,
            transport_encoding=_get_encoding_from_headers(self.headers),
            namespaceHTMLElements=False,
        )
        base_url = _determine_base_url(document, self.url)
        for anchor in document.findall(".//a"):
            if anchor.get("href"):
                href = anchor.get("href")
                url = _clean_link(urllib_parse.urljoin(base_url, href))
                pyrequire = anchor.get('data-requires-python')
                pyrequire = unescape(pyrequire) if pyrequire else None
                yield Link(url, self.url, requires_python=pyrequire)

use_pep517=use_pep517,
            constraint=constraint, isolated=isolated, wheel_cache=wheel_cache
        )

    # parse a nested requirements file
    elif opts.requirements or opts.constraints:
        if opts.requirements:
            req_path = opts.requirements[0]
            nested_constraint = False
        else:
            req_path = opts.constraints[0]
            nested_constraint = True
        # original file is over http
        if SCHEME_RE.search(filename):
            # do a url join so relative paths work
            req_path = urllib_parse.urljoin(filename, req_path)
        # original file and nested file are paths
        elif not SCHEME_RE.search(req_path):
            # do a join so relative paths work
            req_path = os.path.join(os.path.dirname(filename), req_path)
        # TODO: Why not use `comes_from='-r {} (line {})'` here as well?
        parsed_reqs = parse_requirements(
            req_path, finder, comes_from, options, session,
            constraint=nested_constraint, wheel_cache=wheel_cache
        )
        for req in parsed_reqs:
            yield req

    # percolate hash-checking option upward
    elif opts.require_hashes:
        options.require_hashes = opts.require_hashes

use_pep517=use_pep517,
            constraint=constraint, isolated=isolated, wheel_cache=wheel_cache
        )

    # parse a nested requirements file
    elif opts.requirements or opts.constraints:
        if opts.requirements:
            req_path = opts.requirements[0]
            nested_constraint = False
        else:
            req_path = opts.constraints[0]
            nested_constraint = True
        # original file is over http
        if SCHEME_RE.search(filename):
            # do a url join so relative paths work
            req_path = urllib_parse.urljoin(filename, req_path)
        # original file and nested file are paths
        elif not SCHEME_RE.search(req_path):
            # do a join so relative paths work
            req_path = os.path.join(os.path.dirname(filename), req_path)
        # TODO: Why not use `comes_from='-r {} (line {})'` here as well?
        parsed_reqs = parse_requirements(
            req_path, finder, comes_from, options, session,
            constraint=nested_constraint, wheel_cache=wheel_cache
        )
        for req in parsed_reqs:
            yield req

    # percolate hash-checking option upward
    elif opts.require_hashes:
        options.require_hashes = opts.require_hashes

def _url_for_path(self, path):
        # type: (str) -> str
        return urllib_parse.urljoin(self.url, path)