Zeller's Congruence - Coded in Python

#!C:\Python37\python

# 1 2 3 4 5 6

# ...56789012345678901234567890123456789012345678901234567890...

# C:\Users\DCarew\py3dev\ZellersC_1arg.py

#

# Compute day-of-the-week for given date using Zeller's Congruence

# URL Wikipedia reference to Zeller's formula is:

# https://en.wikipedia.org/wiki/Zeller%27s_congruence

#

# Note: date m/b YYYYMMDD format, one cmd-line arg: -dYYYYMMDD

# Note2: there is simpler, near-nocode way to do this using python library

# import code (i.e. calendar and perhaps datetime). This program is

# by way of experimenting w/ Zeller's Congruence.

#

# SLIME TRAIL (change history)

#

# DATE WHO DESCRIPTION

# ======= ======= =========================================

# 08/22/2023 See URL hoping this works 'cuz it will be hell to debug otherwise

# URL is: https://stackoverflow.com/questions

# /46002047/day-of-the-week-using-zellers-congruence-

# -python-3

# 10/25/2023 carew Modify to accept single command-line arg in format YYYYMMDD

# 12/13/2024 carew Modify for 70-char width (to fit neatly in a Wix weblog post...

# TO DO: #####################################################################

import argparse

import datetime

import sys

def valid_date(d):

"""

Use datetime library validation to check arg passed in

"""

try:

fulldt = datetime.datetime.strptime(d, "%Y%m%d")

except ValueError:

msg = "Not a valid date: '{0}'.".format(d)

raise argparse.ArgumentTypeError(msg)

return d

# main starts here

parser = argparse.ArgumentParser(prog='ZellersC_1arg',

description="Find calendar day-of-week for 'any' date yrs 1583-9999")

parser.add_argument('-d', "--yyyymmdd",

help="Zeller's Congruence Date - format YYYYMMDD ",

required=True,

type=valid_date)

args = parser.parse_args()

yyyymmdd_dt = args.yyyymmdd

# diagnostics below commented out

# print(" year is: ", yyyymmdd_dt[:4])

# print("month is: ", yyyymmdd_dt[4:6])

# print(" day is: ", yyyymmdd_dt[6:8])

year = int(yyyymmdd_dt[:4])

if year not in range(1583, 10000):

print("Year is out of allowed range 1583 - 9999. Please enter \

valid date arg as -dYYYYMMDD")

sys.exit(2)

month = int(yyyymmdd_dt[4:6])

if month not in range(1, 13):

print("Month is out of allowed range 1 - 12. Enter valid date \

as -dYYYYMMDD")

sys.exit(2)

if month == 1 or month == 2:

month += 12

year -= 1

# adjust month, year numbers for the formula from Wikipedia

day = int(yyyymmdd_dt[6:8])

if day not in range(1,32):

print("day is not good value for of month (1 - 31). \

Please enter date as digits -dYYYYMMDD ")

sys.exit(2)

kay = int(year % 100)

# kay is K century number-- see Gregorian calendar

# formula is in above wikipedia URL reference.

jay = int(year // 100) # jay is J zero-based century number. See

# Wikipedia reference.

# Below is my code to execute the wikipedia formula:

result = (day + (13 * (month+1) // 5) + kay + (kay // 4) + \

(jay // 4) - (2*jay))

result = result % 7

# print("result is: ",result) # diagnostic commented out

weekday = {0:"Saturday", 1:"Sunday", 2:"Monday", 3:"Tuesday",\

4:"Wednesday", 5:"Thursday", 6:"Friday"}

# print("The day of the week for date " + yyyymmdd_dt + " is: " + \

# weekday[int(result)] + ".")

# ...more 'sophisticated' formatting below

print(f"The day of the week for date %4d-%2.2d-%2.2d is: \

{weekday[int(result)]}." % (year,month,day))

---

Copy the above code and paste it into Notepad (or any editor's blank buffer). Save the code under {whatever-name-you-wish}.py

Run the code using the python launcher "py". Here is an example showing that D-Day was a Tuesday:

$>py -3 ZellersC_narrow_1argp3v3.py -d 19440606

The day of the week for date 1944-06-06 is: Tuesday.

Note: the code is formatted in a terrible, squirrelly way, because Wix text entry is not ideal for entering code-- HOWEVER, I did carefully test it by extracting the source from the above code section, and for me it ran, in spite of non-attractive formatting.