для суммирования времени (например ".5:15 + 1:: + 30: = 01:30:45")

time_sum.py

# -*- coding: utf-8 -*-
"""

"""

# for python2
from __future__ import print_function
input = vars(__builtins__).get('raw_input',input)

def ask_times():
    while (True):
        try:
            time = input(' + ')
        except (EOFError, KeyboardInterrupt):
            break
        if 0<len(time):
            yield time
        else:
            break

def sec_from_time(time):
    parts = time.split(':')
    parts.reverse()
    level = 1
    ret = 0
    for part in parts:
        if len(part):
            ret += float(part) * level
        level *= 60
    return ret

def time_from_sec(sec):
    parts = []    
    sec_remain = float(sec)
    while(sec_remain):
        if 60 > sec_remain:
            part = sec_remain
            sec_remain = 0
        else:
            part = float(sec_remain % 60)
            sec_remain = float(int(sec_remain/60))
        parts.append(part)
    parts.reverse()
    return ':'.join(map(lambda p: '{:02.4n}'.format(p), parts))

sum_sec = 0    
for time in ask_times():
    sum_sec += sec_from_time(time)
    print(' = ', time_from_sec(sum_sec))