humanize elapsed time

elapsed_time.py

def elapsed_time(start, end):
    """
    >>> from datetime import datetime
    >>> elapsed_time(datetime(2000, 1, 1), datetime(2000, 1, 1, 20, 15))
    '20 hours, and 15 minutes'
    >>> elapsed_time(datetime(2000, 1, 1), datetime(2000, 1, 1, 0, 1))
    '1 minute'
    >>> elapsed_time(datetime(2000, 1, 1), datetime(2000, 1, 2, 0, 1))
    '1 day, and 1 minute'
    >>> elapsed_time(datetime(2000, 1, 1), datetime(2000, 1, 2, 2, 3, 4))
    '1 day, 2 hours, 3 minutes, and 4 seconds'
    """

    assert start < end

    td = end - start
    out = []
    if td.days:
        out.append('%d day%s' % (td.days, 's' if td.days > 1 else ''))

    modulor = td.seconds
    moduland = 3600
    for label in ('hour', 'minute', 'second'):
        amount, modulor = divmod(modulor, moduland)
        if amount:
            out.append('%d %s%s' % (amount, label, 's' if amount > 1 else ''))
        moduland /= 60

    if len(out) > 1:
        out[-1] = "and %s" % out[-1]
    return ', '.join(out)