Calculate Difference Between Dates

# A script for calculating the difference between two dates in years, months, and days.


# Function definitions:


# Function to ask user for dates and assign them to variables.

def input_dates():

    print "What is the start date?"

    # gets user input for start date in 3 separate variables

    start_month = raw_input("Month: ")
    start_day = raw_input("Day: ")
    start_year = raw_input("Year: ")


    print "\nThat's a dope ass date. Now what's the end date?"

    # gets user input for end date in 3 separate variables

    end_month = raw_input("Month: ")
    end_day = raw_input("Day: ")
    end_year = raw_input("Year: ")


    start_date = [start_month, start_day, start_year] # stores start date variables in a single list
    end_date = [end_month, end_day, end_year] # stores end date variables in a single list


    return (start_date, end_date) # returns start date and end date as lists


# Function to find the difference between two dates

def date_difference(date1, date2):


# assign variables to start year, end year, and their difference

    year1 = int(date1[2])
    year2 = int(date2[2])
    year_diff = year2 - year1

# assign variables for days

    day1 = int(date1[1])
    day2 = int(date2[1])


# assign a list variable containing all months to reference via index

    months = ["January", "February", "March", "April", "May", "June", "July",
            "August", "September", "October", "November", "December"]


# assign string variable to user month inputs

    month1 = date1[0] # defines start month as first string in start date list
    month2 = date2[0] # defines end month as first string in end date list


# iterates through months list until matching month is found for start month

    for month in months:
        if month != month1:
            continue
        month_num1 = int(months.index(month)) # assigns integer value to month after match is found


# iterates through months list until matching month is found for end month

    for month in months:
        if month != month2:
            continue
        month_num2 = int(months.index(month)) # assigns integer value to month after match is found

    # print month_num1 # check loop
    # print month_num2 # check loop

# finds month difference.

    if month_num2 < month_num1: # accounts for case when end month precedes start month in end year
        month_diff = 12 - (month_num1 - month_num2)
        year_diff -= 1 # subtracts one year from total if end month precedes start month in end year
    elif month_num2 > month_num1:
         month_diff = month_num2 - month_num1
    else: # special cases for when the start month and end month are the same
        if day2 >= day1:
            month_diff = 0
        else:
            month_diff = 11
            year_diff -= 1



# assigns a value for the number of days in the month prior to the end month. necessary to calculate day difference

    if month_num2 in (0,1,3,5,7,8,10):
        month_len = 31
    elif month_num2 in (4,6,9,11):
        month_len = 30
    else: # checks if leap year for February days
        if (year2 % 4 == 0 and year2 % 100 != 0) or year2 % 400 == 0: # this is the necessary condition for a leap year to exist
            month_len = 29
        else:
            month_len = 28



# finds day difference. accounts for preceding day numbers in later months e.g. june 20 to march 2

    if day2 < day1:
        day_diff = month_len + day2 - day1
    else:
        day_diff = day2 - day1


# prints difference in years, months, and days.

    print "\nWow. Thats %d years, %d months, and %d days!\n" % (year_diff, month_diff, day_diff)

# returns values to be used for total days calculation

    return (year_diff, day_diff, year1, year2, day1, day2, month_num1, month_num2, months)


# used to check calculations and variable values for debugging

""" # check variable values
    print month_num1
    print month_num2
    print month_len
    print year_diff
    print day1
    print day2
    print month_diff
    print day_diff """



# Function to calculate total number of days. Will take all return values from date_difference function

def total_day_count(years, days, year1, year2, day1, day2, month1, month2, months):


    year_days = years * 365 # calculates number of days contained in full years


# finds number of days in month prior to end month, adds remaining number of days from start date to total days


    if month2 in (0,1,3,5,7,8,10):
        month_end_len = 31
    elif month2 in (4,6,9,11):
        month_end_len = 30
    else: # checks if leap year for February days
        if (year2 % 4 == 0 and year2 % 100 != 0) or year2 % 400 == 0:
            month_end_len = 29
        else:
            month_end_len = 28


    # print month2 # check variable
    # print month_end_len # check variable


    total_days = year_days + (month_end_len - day1) + day2 # starts day total with complete year days plus days in start and end months

    # print total_days # check calculation



# the next two loops calculate the number of days in all the months between start and end month. adds days to total at every loop iteration


# first case: when the end month precedes start month in end year e.g. june 2014 to april 2015

    if month2 < month1:
        for month in range(month1+1, 12): # loops over all months between start month and end of year, excluding start month
            if month in (0,2,4,6,7,9,11):
                month_len = 31
                total_days += month_len
            elif month in (3,5,8,10):
                month_len = 30
                total_days += month_len
            else: # if the month is February, it checks for a leap year then assigns the month length
                if (year1 % 4 == 0 and year1 % 100 != 0) or year1 % 400 == 0:
                    month_len = 29
                    total_days += month_len
                else:
                    month_len = 28
                    total_days += month_len

        for month in range(0, month2): # loops over all month between beginning of year and end month, excluding end month
            if month in (0,2,4,6,7,9,11):
                month_len = 31
                total_days += month_len
            elif month in (3,5,8,10):
                month_len = 30
                total_days += month_len
            else: # same February calculation as above
                if (year1 % 4 == 0 and year1 % 100 != 0) or year1 % 400 == 0:
                    month_len = 29
                    total_days += month_len
                else:
                    month_len = 28
                    total_days += month_len


# second case: when end month is after start month in later year e.g. june 2014 to august 2015

    if month2 > month1: # loops over all months between start month and end month. excluding start and end months
        for month in range(month1+1, month2):
            if month in (0,2,4,6,7,9,11):
                month_len = 31
                total_days += month_len
            elif month in (3,5,8,10):
                month_len = 30
                total_days += month_len
            else:
                if (year1 % 4 == 0 and year1 % 100 != 0) or year1 % 400 == 0:
                    month_len = 29
                    total_days += month_len
                else:
                    month_len = 28
                    total_days += month_len

# third case: when end month and start month are the same.

    if month2 == month1 and years == 0:
        total_days = 365 + (day2 - day1)

    if month2 == month1 and years != 0:
        total_days = (years * 365) + (365 + (day2 - day1))



# adds days for leap years that are present in the year span.

    for year in range(year1, year2): # the end year isn't included because February would already be accounted for in the month days calculation above
        if (year % 4 == 0 and year % 100 != 0) or year % 400 == 0:
            total_days += 1
            # print year # check loop


    print "Damn son. That's %d days!\n" % total_days # prints total days


    return (total_days) # returns total days for conversion


# Function to convert total days to other units of time and print them

def convert(days):

    hours = days * 24
    minutes = hours * 60
    seconds = minutes * 60
    weeks = days / 7
    extra_days = days % 7
    hexsecs = float(seconds * 1.32)

    print "If you wanna get wild, that's equal to:\n"
    print "%d hours" % hours
    print "%d minutes" % minutes
    print "%d seconds" % seconds
    print "%d weeks and %d days" % (weeks, extra_days)
    print "And %d hexadecimal seconds! (wtf is that anyway?)\n" % hexsecs


# end function definitions



# start script


print "\nOh shit. You have to go to China on a secret mission?! How long are you gonna be there?\n"


# calls functions and assigns variables to return values

(start, end) = input_dates()

(years, days, year1, year2, day1, day2, month1, month2, months) = date_difference(start, end)

total_days = total_day_count(years, days, year1, year2, day1, day2, month1, month2, months)

convert(total_days)