def geturl(url_set, url, default):
    u = getattr(settings, url, default)
    if re.match("^[a-zA-Z0-9_.-]+$", u) is not None and u not in url_set:
        url_set.append(u)
    else:
        raise ImproperlyConfigured('The url "%s" is already in use' % u)
    return u
It checks if the url is valid and not already in use, in case
dataset/ETHPy150Open wtrevino/django-djobberbase/djobberbase/conf/settings.py/geturl