This year Christmas Eve is a Sunday
Can anyone write a script to determine the years in which Christmas Eve falls on a Sunday?
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The Bing bot provided this Python script. It seems to work for me.
import datetime
for year in range(1900, 2101):
christmas_eve = datetime.date(year, 12, 24)
if christmas_eve.weekday() == 6:
print(year)
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Seems us scriptwriters have been redunded by AI
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Here is a bash script that determines the years in which Christmas Eve falls on a Sunday:
#!/bin/bash
for year in {1901ā¦2099}
do
if [[ $(date -d ā${year}-12-24ā +%A) == āSundayā ]]
then
echo ā$yearā
fi
done
This script uses the date command to check the day of the week for December 24th of each year between 1901 and 2099. If the day is Sunday, the year is printed to the console. You can modify the range of years by changing the values in the curly braces. Itās also provided by Bing AI Chat.
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Thanks. For me, bash script is easier to understand than python.
Both python and bash versions use a ādateā function.
Is anyone keen enough to understand the calendar maths
and do it from scratch?
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Does this still work based on system date on mac and pc given that there is a confusion between them about the year 1900 and 1904 being a leap year or not.
Not important for me, just remember when using excel date on the 2 systems can give different results.
1900 is not a leap year
"The rule is that if the year is divisible by 100 and not divisible by 400, leap year is skipped. "
But what is this about 1904? That should be a normal
leap year
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During my time at apple we had a great discussion regarding date differences from mac to pc and who was correct about 1900 and 1904 as excel on the two products gave different results
I cannot find the original article but this link covers most of it
Yes know the calculation for leap years
To be a leap year, the year number must be divisible by four ā except for end-of-century years, which must be divisible by 400. This means that the year 2000 was a leap year, although 1900 was not.
2024, 2028, 2032 and 2036 are all leap years.
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I get it, Msoft took a shortcut to help machines with limited
calculating power. ā¦ and it came back to haunt them.
I hope it is fixed today.
Maybe sometime over the long holiday weekend I can try to cook up a BASIC version without the aid of Bingbot. 
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The only āY2K bugā I found - post-mortem - was a developer assumed that 2000 was not a leap year, thus only 28 days in February 2000, when 29/02/2000 rolled around it caused havoc in my customerās ābespokeā mortgage management system 
ā¦
Fortunately for them (the customer) the developer was available to re-write his shonky codeā¦ He was a half decent bloke, but still billed them for the āre-writeā (Iād probably have done the same - they [customer] were very laccadaisical in their specification design document).
Canāt remember what the programming language was - I think Visual Basic. Backend was SQL Server - which was my involvement - yeah - I used to do Windows stuff on SQL Serverā¦ Iād done a bit with Sybase (which Microsoft paid to have ported to Windows NT - thatās how we got SQL Server) before. Unfortunately - was never able to cross-skill in Oracle RDBMS where all the $$$ in consulting is locatedā¦
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So much talk about no room for all the planes that could not fly due to the y2k bug. I was working in a hospital IT department at that time and the lead up to it was massive. In the end no big deal, i even went on call for that night but nothing.
I am starting to prepare for the next big deal of 9999 but guess may not see it.
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Here is a Powershell version I came up with myself.
$c = 0
$s = @()
for ($y = 1900; $y -le 2101; $y++) {
$d = 358
if ($y % 4 -eq 0) {
$d = 359
}
if ($y % 100 -eq 0) {
$d = 358
}
if ($y % 400 -eq 0) {
$d = 359
}
$c = $c + $d
$w = $c % 7
if ($w -eq 0) {
$s += [PSCustomObject]@{
Year = $y
Day = $d
Weekday = $w
}
}
}
$s | Format-Table -AutoSize
For each year from 1900 through 2101 it decides if it is a leap year or not. Christmas Eve is either day 358 or 359 of the year. Then the running total of the number of days since 1/1/1900 is used to calculate the remainder of the cumulative days divided by 7. That gives the day of the week. If the day of the week is 0 it is Sunday. Those days are added to a PSCustomObject and displayed in a table at the end.
I checked the 28 years listed in the output against https://www.timeanddate.com and those years are correct. There may be other years that are not listed but did fall on a Sunday. Maybe someone could come up with a proof, but I trust it. It does match the output from the earlier Python script.
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I shall run itā¦ not in Powershellā¦ it should go in csh or sh
The algorithm seems reasonableā¦ you just count your way up from a known base.
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Well before 9999, thereās the UNIX 2038 date bugā¦
Year 2038 problem - Wikipedia.
I will be 76 in 2038 - if I make it that far (my Tripp great great grandfather, a convict, lived into his 80ās but since then all his Tripp male descendants barely get to, or past 65 - e.g. my dad died two months before his 67th birthday)ā¦
I was working in a hospital IT department, leading up to Y2K - but left in early 1999 - we (my boss) hired several contractors just to do Y2K testingā¦
I went to another āhealth relatedā environment, mostly SCO UNIX running across West Australiaās regional centres (WA regional hospitals ran much of their stuff, back then, on Progress āflat fileā database systems hosted on SCO Openserver - and many users connected via dumb ascii terminals over serial lines to Stallion āpaddle boardsā).
One morning I came into the office**, and thereād been a power outage, which the UPS didnāt āweatherāā¦ I noticed a couple of the systems in the ālab / server roomā had the wrong date - so I set them to the correct date - only to learn - that was deliberate - they had the wrong date 'cause they were using them to test Y2K rollover! One was SCO OpenServer on a Pentium Pro server, the other one was SunOS 4x on Sun hardware - both to run these ghastly Progress RDBMS applications (I donāt think it was an IPX, probably an SS5 or SS4 maybe? I just looked at the price for an NVRAM battery to I can fire up my SparcStation IPX - $200 USD for a wonky little battery??? No! I guess I will continue to consider it a doorstop or monitor stand).
** the only thing I miss about that job - I HAD MY OWN OFFICE just for ME with a door! Thatās the ONLY time Iāve ever had that luxury!
3 Likes
I tried it in bash.
Required some considerable modification, since the way bash handles arithmetic
is arcane, to say the least.
My rough bash version
#!/bin/bash
# sunday christmas eve
c=0;
for y in $@
do d=358;
if (( $y % 4 == 0 )); then
d=359
fi
if (( $y % 100 == 0 )) then
d=358
fi
if (( $y % 400 == 0 )) then
d=359
fi
c=`expr $c + $d`
w=`expr $c % 7`
if (( $w == 0 )) then
echo $y; echo $d; echo $w;
fi
done
It does not do the years loop. You can achieve that with
$ ./sunday `seq -s " " 1900 2100` >out
I get 28 years, including 2023 , so I guess it is correct.
Note:
If anyone wants to try numerical calculations in a bash script, have a look at
@abhishek 's excellent bash tutorial
You need examples.
There is an algorithm invented by Gauss which calculates āday of weekā for any
nominal date. It is in Wikipedia
It does not count from a known base, but it uses modulus in the same way that you do.
You are in good company.
4 Likes
There are some quite sophisticated algorithms for determining day of the week from date.
Here is one coded in R
function(y, m, d )
# dayofweek(y,m,d)
# Sakamoto's algorithm for day of week
# 1 <= m <= 12 , y > 1752 (in UK)
# returns 0=Sunday, 1=Monday, ...
{
t <- c(0,3,2,5,0,3,5,1,4,6,2,4)
if (m < 3) {
y <- y - 1
}
return (as.integer((y + y/4 - y/100 + y/400 + t[m] + d) %% 7))
}
We can use it to look at which Christmas Eveās are Sundays by writing a simple calling function
function(y)
# cesunday() Years in which Christmas Eve is on a Sunday
{
for(i in 1:length(y)) {
if(dayofweek(y[i],12,24) == 0) {
print(y[i])
}
}
}
and we can run it like this
> cesunday(seq(1900,2025))
[1] 1905
[1] 1910
[1] 1916
[1] 1927
[1] 1933
[1] 1944
[1] 1950
[1] 1955
[1] 1961
[1] 1967
[1] 1972
[1] 1978
[1] 1989
[1] 1995
[1] 2000
[1] 2006
[1] 2012
[1] 2017
[1] 2023
which seems to be correct.
3 Likes
Its the first time i have come across the 2038 issueā¦ do you think 32 bit systems will still be around then
As i will be 80 at that point not sure i need to worry too much perfer to think of the feast of end of life windows 10 later this year and how much i may make, thanks microsoft for printing money for people like myself
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The interval between years with Christmas Eve on a Sunday
seems to vary between 5 and 11 years.
Can anyone explain why it is restricted to that range of
numbers?
Or is it?.. better look at a wider range of years.
I checked from 1800 to 2200 and the min is 5 and max is 12. Same for years 1000 to 3000. The calculation may not be completely valid for extremely past or future dates.
Interesting question.
Iām guessing that each year it basically moves by one day, but then leap year messes it up and may skip Sunday once every so often. Thatās why it is 11 or 12 maybe. From that line of thinking it should max out at 13. If it just missed it one year and then skips it in 7 that would be 13 I think.
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