>>> def frac(n):
... i = int(n)
... f = round((n - int(n)), 4)
... return (i, f)
...
>>> frac(53.45)
(53, 0.45) # A tuple
>>> def frmt(hour): # You can rewrite it with 'while' if you wish
... hours, _min = frac(hour)
... minutes, _sec = frac(_min*60)
... seconds, _msec = frac(_sec*60)
... return "%s:%s:%s"%(hours, minutes, seconds)
...
>>> frmt(72.345)
'72:20:42'
>>> l = [72.345, 72.629, 71.327]
>>> map(frmt, l)
['72:20:42', '72:37:44', '71:19:37']