hours (h) calculated by floor division (by //) of seconds by 3600 (60 min/hr * 60 sec/min)
minutes (m) calculated by floor division of remaining seconds (remainder from hour calculation, by %) by 60 (60 sec/min)
similarly, seconds (s) by remainder of hour and minutes calculation.
Rest is just string formatting!
def hms(seconds):
h = seconds // 3600
m = seconds % 3600 // 60
s = seconds % 3600 % 60
return '{:02d}:{:02d}:{:02d}'.format(h, m, s)
print(hms(7500)) # Should print 02h05m00s