print a duration in human readable format

Duration.py

import datetime
import time

class Duration:
    def __init__(self, start_time=None, end_time=None):
        self.start_time = start_time
        self.end_time = end_time

    def start(self):
        self.start_time = time.time()

    def stop(self):
        self.end_time = time.time()

    def print_duration(self):
        duration = self.end_time - self.start_time
        print str(datetime.timedelta(seconds=int(duration)))


d = Duration()
d.start()
time.sleep(3)
d.stop()
d.print_duration()