I'm looking to trigger a script on the 4th day before the end of the month. Can a setup like this work where I check if the result of a task is True to run the rest or do I need a different approach? Thanks!

I don't think that will work since the return type of

execution_day

is a

Task

in the

Flow

context. The blunt way would be to just fail the task (raise an exception or something) if the day is not right.

That won't work since you're trying to evaluate the task when the flow is created, rather than when it is run. Take a look at say, using `case`: https://docs.prefect.io/core/idioms/conditional.html

Hi @Jelle Vegter! Have you looked at adding “filters” and “adjustments” to your schedule? This is a bit advanced, and you can find the docs here: https://docs.prefect.io/core/concepts/schedules.html. What I have in mind is that you would make a daily

Clock

(so a candidate event is created for every day), then use

filters.is_month_end

to only keep the candidate events corresponding to the end of the month, then use

adjustments.add

to add negative four days to the candidate event. The final event would be 4 days prior to a month end. Recognizing that this is a little convoluted, I do have good news: we are actively working on schedule enhancements that anticipate your use case in a more first class way.

Can you simply express the “4th-from-month-end” in the

cron

syntax?

@Wilson Bilkovich thanks! I actually wasn’t familiar with cron relative syntax. @Jelle Vegter ^ this is a better approach than my recommendation

I love cron, but I still have to ponder for a minute to remember what the positions do.. I should use it more often until that goes away.

@Wilson Bilkovich are you sure this works? I remember trying the L-4 statement without it working. Could be that I made a mistake trying it out though!

It may not work with the CronClock library; should work in regular cron implementations

Looks like we don’t support the L-4 state on the UI. Will try on the API

CronClock

uses

croniter

under the hood and it looks like the syntax is either

#<number>

or

L<number>

according to its docs https://github.com/kiorky/croniter#usage

Seems both #4 and L4 are not supported in the UI and API. It would make this significantly easier. Jeremiah’s approach with adjustments might be the best for now. I’ll open a ticket for this Cron syntax.

Awesome, thanks. for now I just added a case statement and a task to check if the date is 4 before before the end. Thanks all!

ponder for a minute

Is that

* * * * *

?

I wonder if:

0 8 24-27 * * [ `/bin/date -d +4day +\%d` -eq 1 ]

would work? That’s another slightly-more-standard-ish way to express it

I looked into this and we just pass the Cron expression to

croniter

.

croniter

has an example

iter = croniter('0 0 * * 5#3,L5', base)

like what Jeremiah suggested, but I tried this out using

print(croniter.is_valid("0 0 * * 5#3,L5"))

and it printed False…. So I think this might be more on an issue with

croniter

. I’ll open an issue on their repo.