Parse url URL parameter.

def parse_url(request, url):
    """Parse url URL parameter."""
    try:
        validate = URLValidator()
        validate(url)
    except ValidationError:
        if url.startswith('/'):
            host = request.get_host()
            scheme = 'https' if request.is_secure() else 'http'
            url = '{scheme}://{host}{uri}'.format(scheme=scheme,
                                                  host=host,
                                                  uri=url)
        else:
            url = request.build_absolute_uri(reverse(url))
    return url