def _andlist(ss, sep=', ', seplast=', and ', septwo=' and '):
    """Comma-separate a list of strings according to English rules.

    Enforces the Oxford comma.
    """
    if len(ss) <= 1:
        return ''.join(ss)
    if len(ss) == 2:
        return septwo.join(ss)
    return sep.join(ss[:-1]) + seplast + ss[-1]
