Calculating Weekdays

from datetime import date
import random
import time

try:    input_func=raw_input
except: input_func=input


#Coded by Ian Mallett
#   http://pastebin.com/eGWj0TNK

def calculate_is_leapyear(year):
    is_leapyear = False
    if year%4==0:
        is_leapyear = True
        if year%100==0:
            is_leapyear = False
            if year%400==0:
                is_leapyear = True
    return is_leapyear
def calculate_weekday(year,month,day):
    #Execute algorithm you should use to mentally calculate any day-of-the-week.  It is the easiest known.
    #   See http://firstsundaydoomsday.blogspot.com/2009/12/quick-start-guide.html
    #   In the below, I mod by 7 after every step, but you can do this all at once at the very end if you'd
    #   prefer.  An easy way to mod by 7 is to subtract multiples of 7.  7, 14, 21, 28, 35, 42, 49, 56,
    #   and 63 are the useful multiples here.

    #============================================
    #1. Calculate if is leapyear
    is_leapyear = calculate_is_leapyear(year)

    #============================================
    #2. Add offset due to year
    T = year % 100 #last two digits of year
    if T%2==1: #last two digits odd
        T += 11
    T //= 2 #"T" is even at this point.  Divide it by 2.
    if T%2==1: #"T" is odd
        T += 11 #or add 4, since about to mod
    T %= 7

    #============================================
    #3. Add century's first Sunday (CFS)
    #   0     2    4    5
    #--------------------
    #  n/a  n/a 1500 1600
    # 1700 1800 1900 2000
    # 2100 2200 2300 etc.
    #The delineation between Julian and Gregorian calendars is fuzzy based on location.  E.g. in Italy,
    #   where the change from Julian to Gregorian was invented/mandated, it was 1582.  In
    #   England/colonies, it was 1752.  Here's the whole gory thing: http://norbyhus.dk/calendar.php
    is_gregorian = year >= 1582 #Italy-centric
    if is_gregorian: #Newer, Gregorian calendar
        if   year>=1500 and year<=1599: T+=4
        elif year>=1600 and year<=1699: T+=5
        elif year>=1700 and year<=1799: T+=0
        elif year>=1800 and year<=1899: T+=2
        elif year>=1900 and year<=1999: T+=4
        elif year>=2000 and year<=2099: T+=5
        elif year>=2100 and year<=2199: T+=0
        elif year>=2200 and year<=2299: T+=2
        elif year>=2300 and year<=2399: T+=4
        else: assert False
    else: #Older, Julian calendar
        T += year // 100
    T %= 7
    #Note that you can memorize the values of "T" up to here for years you care about.  For example,
    #   for 2015, "T" is 1.  Then, if you were given a date in 2015, you could just jump to here.

    #============================================
    #4. Add Month's doomsday
    #   If January, February, or March, use memorized values
    #   Otherwise:
    #       If even-numbered month, use month number
    #       If odd-numbered month, use the unordered pairs (5,9) and (7,11) (that is, 5->9,9->5 and 7->11,11->7)
    if   month ==  1: #January
        if is_leapyear: T+=4
        else:           T+=3
    elif month ==  2: #February
        if is_leapyear: T+=1
        else:           T+=0
    elif month ==  3: T+= 0 #March
    elif month ==  4: T+= 4 #April
    elif month ==  5: T+= 9 #May
    elif month ==  6: T+= 6 #June
    elif month ==  7: T+=11 #July
    elif month ==  8: T+= 8 #August
    elif month ==  9: T+= 5 #September
    elif month == 10: T+=10 #October
    elif month == 11: T+= 7 #November
    elif month == 12: T+=12 #December
    else: assert False
    T %= 7

    #============================================
    #5. Subtract total from day
    T = day - T
    T %= 7

    #============================================
    #6. Done!  Convert T into weekday and output.
    if T<0: T+=7
    #              0        1         2          3           4         5         6
    weekdays = ["Sunday","Monday","Tuesday","Wednesday","Thursday","Friday","Saturday"]

    #============================================
    #Check answer using Zeller's Congruence (simpler, but harder to do mentally)
    #   See https://en.wikipedia.org/wiki/Zeller%27s_congruence
    m = month
    y = year
    if m<3:
        #See http://stackoverflow.com/questions/16376684/is-there-formula-to-calculate-what-day-is-for-anyday-i-got-stuck-by-project-eul
        m += 12
        y -= 1
    K = y % 100
    J = y // 100
    if is_gregorian:
        h = (day + int(13.0*(m+1)/5.0) + K + int(K/4.0) + int(J/4.0) + 5*J) % 7
    else:
        h = (day + int(13.0*(m+1)/5.0) + K + int(K/4.0) + 5 + 6*J) % 7
    d = (h+6) % 7
    assert weekdays[T] == weekdays[d]

    #============================================
    #Return
    return weekdays[T]
def output_weekday(year,month,day):
    weekday = calculate_weekday(year,month,day)
    print("Weekday for %04d-%02d-%02d: %s"%(year,month,day,weekday))

def test():
    #Thursday
    output_weekday(1776,7,4) #United States Independence Day

    #Wednesday
    output_weekday(1895,5,1)

    #Saturday
    output_weekday(1962,8,4)

    #Sunday
    output_weekday(1941,12,7) #Pearl Harbor Day

    #Sunday
    output_weekday(1899,12,31)

    #Monday
    output_weekday(1900,1,1) #The next day

    #Saturday
    output_weekday(1066,10,14) #Battle of Hastings (note Julian calendar)

def quiz():
    while True:
        year = random.randrange(1582,2399+1,1)
        is_leapyear = calculate_is_leapyear(year)

        month = random.randrange(1,12+1,1)
        if   month== 1: day=random.randrange(1,31+1,1)
        elif month== 2:
            if is_leapyear: day=random.randrange(1,28+1,1)
            else:           day=random.randrange(1,29+1,1)
        elif month== 3: day=random.randrange(1,31+1,1)
        elif month== 4: day=random.randrange(1,30+1,1)
        elif month== 5: day=random.randrange(1,31+1,1)
        elif month== 6: day=random.randrange(1,30+1,1)
        elif month== 7: day=random.randrange(1,31+1,1)
        elif month== 8: day=random.randrange(1,31+1,1)
        elif month== 9: day=random.randrange(1,30+1,1)
        elif month==10: day=random.randrange(1,31+1,1)
        elif month==11: day=random.randrange(1,30+1,1)
        elif month==12: day=random.randrange(1,31+1,1)

        weekday = calculate_weekday(year,month,day)

        current_date = date.today()
        if year==current_date.year and month==current_date.month and day==current_date.day:
            s = "What day of the week is it today, "
        elif year<current_date.year or (year==current_date.year and (month<current_date.month or (month==current_date.month and day<current_date.day))):
            s = "What day of the week was it on "
        else:
            s = "What day of the week will it be on "
        s += "%04d-%02d-%02d?  ENTER to get answer." % (year,month,day)
        t0 = time.time()
        input_func(s)
        print("\tIt is/was a %s."%weekday)
        t1 = time.time()
        print("\t%f seconds"%(t1-t0))
        print("")
quiz()