def format(msg, left_margin=0, right_margin=78):
    """ Format a message by inserting line breaks at appropriate places.  msg
    is the text of the message.  left_margin is the position of the left
    margin.  right_margin is the position of the right margin.  Returns the
    formatted message.
    """
    curs = left_margin
    fmsg = ' ' * left_margin
    for w in msg.split():
        l = len(w)
        if curs != left_margin and curs + l > right_margin:
            fmsg = fmsg + '\n' + ' ' * left_margin
            curs = left_margin
        if curs > left_margin:
            fmsg = fmsg + ' '
            curs = curs + 1
        fmsg = fmsg + w
        curs = curs + l
    return fmsg
