def parse_last_period(last):
    """
    Parse the --last value and return the time difference in seconds.
    """
    wordmap = {'hour': '1h', 'day': '1d', 'week': '1w', 'month': '1m'}
    multmap = {'h': 3600, 'd': 86400, 'w': 604800, 'm': 2592000}
    if last in wordmap:
        last = wordmap[last]
    cat = last[-1:].lower()
    if cat not in multmap:
        raise TypeError
    try:
        num = int(last[:-1])
        if num <= 0:
            raise TypeError
    except ValueError:
        raise TypeError
    diff = num * multmap[cat]
    return diff
