elapsed_time():: Human readable time interval between two values of time.time() ¶

import math
import time
import datetime

def elapsed_time(t0, t1, with_milliseconds=False):
    """
    Human readable time interval between two values of time.time()
    """
    milliseconds, seconds = math.modf(t1 - t0)
    #dt = time.strftime("%H:%M:%S", time.gmtime(seconds))
    dt = "{:0>8}".format(str(datetime.timedelta(seconds=seconds)))
    if with_milliseconds:
        dt += ('%.3f' % milliseconds)[1:]
    return dt

import time, datetime
t0 = time.time()
...

dt = str(datetime.timedelta(seconds=time.time() - t0))