def location_candidates(profile, preferred=None):
    candidates = []
    seen = set()

    def add(val):
        if val is None:
            return
        s = str(val).strip().lower().replace(' ', '_')
        if s and s not in seen:
            seen.add(s)
            candidates.append(s)

    if preferred:
        add(preferred)

    sources = []
    try:
        if profile and profile.connection and profile.connection.location:
            sources.append(profile.connection.location)
    except Exception:
        pass
    try:
        if profile and profile.location:
            sources.append(profile.location)
    except Exception:
        pass

    for source in sources:
        add(getattr(source, 'id', None))
        add(getattr(source, 'country_name', None))
        add(getattr(source, 'name', None))
        add(getattr(source, 'code', None))
        add(getattr(source, 'country_code', None))

    return candidates