def get_time_interval(time1, time2):
    '''get the interval of two times'''
    try:
        #convert time to timestamp
        time1 = time.mktime(time.strptime(time1, '%Y/%m/%d %H:%M:%S'))
        time2 = time.mktime(time.strptime(time2, '%Y/%m/%d %H:%M:%S'))
        seconds = (datetime.datetime.fromtimestamp(time2) - datetime.datetime.fromtimestamp(time1)).seconds
        #convert seconds to day:hour:minute:second
        days = seconds / 86400
        seconds %= 86400
        hours = seconds / 3600
        seconds %= 3600
        minutes = seconds / 60
        seconds %= 60
        return '%dd %dh %dm %ds' % (days, hours, minutes, seconds)
    except:
        return 'N/A'
get the interval of two times