def readable_join(items, conjunction='or'):
    """
    Returns an oxford-comma-joined string with "or."

    E.g., ['thing1', 'thing2', 'thing3'] becomes "thing1, thing2, or thing3".
    """
    if not items:
        return None
    count = len(items)
    if count == 1:
        s = items[0]
    elif count == 2:
        template = u' {} '.format(conjunction)
        s = template.join(items)
    else:
        s = u'{}, {} {}'.format(u', '.join(items[:-1]), conjunction, items[-1])
    return s
