def _urljoin(base, url):
    """
    Construct a full ("absolute") URL by combining a "base URL" with another
    URL. Informally, this uses components of the base URL, in particular the
    addressing scheme, the network location and (part of) the path, to provide
    missing components in the relative URL.

    Additionally, the fragment identifier is preserved according to the HTTP
    1.1 bis draft.

    @type base: C{bytes}
    @param base: Base URL.

    @type url: C{bytes}
    @param url: URL to combine with C{base}.

    @return: An absolute URL resulting from the combination of C{base} and
        C{url}.

    @see: L{urlparse.urljoin}

    @see: U{https://tools.ietf.org/html/draft-ietf-httpbis-p2-semantics-22#section-7.1.2}
    """
    base, baseFrag = urldefrag(base)
    url, urlFrag = urldefrag(urljoin(base, url))
    return urljoin(url, b'#' + (urlFrag or baseFrag))

    Construct a full ("absolute") URL by combining a "base URL" with another
    URL. Informally, this uses components of the base URL, in particular the
    addressing scheme, the network location and (part of) the path, to provide
    missing components in the relative URL.

    Additionally, the fragment identifier is preserved according to the HTTP
    1.1 bis draft.

    @type base: C{bytes}
    @param base: Base URL.

    @type url: C{bytes}
    @param url: URL to combine with C{base}.

    @return: An absolute URL resulting from the combination of C{base} and
        C{url}.

    @see: L{urlparse.urljoin}

    @see: U{https://tools.ietf.org/html/draft-ietf-httpbis-p2-semantics-22#section-7.1.2}
    
stackoverflow/venv/lib/python3.6/site-packages/twisted/web/client.py