My script calculate the difference in 2 time. Like this:
lasted = datetime.strptime(previous_time, FMT) - datetime.strptime(current_time, FMT)
Have you tried using str()?
>>> a = datetime.now()
>>> b = datetime.now() - a
>>> b
datetime.timedelta(0, 6, 793600)
>>> str(b)
'0:00:06.793600'
Alternatively, you can use string formatting:
>>> a = datetime.now()
>>> b = datetime.now() - a
>>> s = b.total_seconds()
>>> '{:02}:{:02}:{:02}'.format(s // 3600, s % 3600 // 60, s % 60)
'00:00:06'