DateDiff | Python Fiddle

# By Websten from forums
#
# Given your birthday and the current date, calculate your age in days. 
# Account for leap days. 
#
# Assume that the birthday and current date are correct dates (and no 
# time travel). 
#

month_lengths = [0,31,28,31,30,31,30,31,31,30,31,30,31]

def is_leap_year(y):
    if y % 400 == 0: #example 2000
        return True
    if y % 100 == 0:  #example 1700
        return False
    if y%4 == 0:
        return True
    return False

def fullYears(year1, year2):
    tdays = 0
    span = year2-year1
    if span > 1:
        span = span + 1
        tyear = year1 + 1
        while tyear < year2:
            if is_leap_year(tyear):
                tdays = tdays + 366
            else:
                tdays = tdays + 365
            tyear = tyear + 1
    return tdays

def rest_of_year(month1, day1, year1):
    days_left = month_lengths[month1] - day1 
    monthN =  month1 + 1
    while monthN <= 12:
        days_left = days_left +  month_lengths[monthN]
        if is_leap_year(year1) and monthN == 2:
            days_left = days_left + 1
        monthN = monthN + 1
    return days_left

def up_to_year(month2,day2,year2):
    monthN = 1
    year_to_date = day2
    while monthN < month2:
        year_to_date = year_to_date + month_lengths[monthN] 
        monthN = monthN + 1
        if is_leap_year(year2) and monthN == 2:
            year_to_date = year_to_date + 1
    return year_to_date

def daysBetweenDates(year1, month1, day1, year2, month2, day2):
    if year1 != year2:
        days = fullYears(year1,year2)
        days2 = rest_of_year(month1, day1, year1)
        days3 = up_to_year(month2,day2,year2)
    else:
        days3 = 0
        sM = month1 + 1
        days = month_lengths[month1] - day1
        days2 = day2
        while sM < month2:
            days3 = days3 + month_lengths[sM]
            if (is_leap_year(year1) and sM==2):
                    days3 = days3 + 1
            sM = sM + 1
    print str(days) + ","  + str(days2) + ","  + str(days3)
    return days + days2 + days3

# Test routine

def test():
    test_cases = [((2012,1,1,2012,2,28), 58), 
                  ((2012,1,1,2012,3,1), 60),
                  ((2011,6,30,2012,6,30), 366),
                  ((2011,1,1,2012,8,8), 585 ),
                  ((1900,1,1,1999,12,31), 36523)]
    for (args, answer) in test_cases:
        result = daysBetweenDates(*args)
        if result != answer:
            print "Test with data:", args, "failed"
        else:
            print "Test with: ", args, " case passed!"

test()

Python Fiddle

Python Cloud IDE