def time_difference(time1, time2):
    start_hour, start_min, start_sec = time1
    end_hour, end_min, end_sec = time2
    lst = []

    if len(time2) <= 0 and len(time1)<= 0:
        return 0
    else:
        a = time2[0]-time1[0]
        b = time2[1]-time1[1]
        c = time2[2]-time1[2]
        x = (a,b,c)
        lst = []
        for i in x:
            if i not in lst:
                lst.append(i)
        return str(lst)

time_difference((1, 2, 3), (13, 12, 11))

12:10:08'

def time_difference(time1, time2):
    start_hour, start_min, start_sec = time1
    end_hour, end_min, end_sec = time2
    lst = []

    if len(time2) <= 0 and len(time1)<= 0:
        return 0
    else:
        a = time2[0]-time1[0]
        b = time2[1]-time1[1]
        c = time2[2]-time1[2]
        x = (a,b,c)
        lst = []
        for i in x:
            if i not in lst:
                lst.append(i)

        return ":".join("{:02d}".format(x) for x in lst)

>>> time_difference((1, 2, 3), (13, 12, 11))
'12:10:08'

>>> from datetime import datetime
>>> str(datetime(2014, 04, 15, 22, 31, 17) - datetime(2014, 04, 15, 11, 46, 39))
'10:44:38'

def time_difference(time1, time2):
    start_hour, start_min, start_sec = time1
    end_hour, end_min, end_sec = time2
    lst = []

    if len(time2) <= 0 and len(time1)<= 0:
        return 0
    else:
        a = str(time2[0]-time1[0])
        b = str(time2[1]-time1[1])
        c = str(time2[2]-time1[2])
        if len(c) < 2:
            c = "0" + c
        if len(b) < 2:
            b = "0" + b
        x = (a,b,c)
        lst = ""
        for i in x:
            lst += i + ":"
        return lst[:-1]

def time_difference(time1, time2):
    totalSecond1 = time1[0] * 3600 + time1[1] * 60 + time1[2]
    totalSecond2 = time2[0] * 3600 + time2[1] * 60 + time2[2]

    diffSeconds = totalSecond2 - totalSecond1
    hours = diffSeconds / 3600
    diffSeconds -= hours * 3600
    minutes = diffSeconds / 60
    diffSeconds -= minutes * 60
    print "%02d:%02d:%02d" % (hours,minutes,diffSeconds)