Hi all! A co-worker is trying to schedule a Flow to run on the 2nd of every month, at 8:00 AM PT. I pointed him to the

IntervalSchedule

with

pendulum

(since that’s what I’ve used for daily/weekly tasks) but he noticed that the results don’t quite line up with what he was expecting:

import pendulum
from prefect.schedules.schedules import IntervalSchedule
from prefect.schedules.clocks import CronClock

# Set our start date.
next_start_date: pendulum.DateTime = (
    pendulum.now(tz="America/Los_Angeles")
    .start_of(unit="month")
    .set(day=2, hour=8, minute=0, second=0)
)

# Set our monthly interval.
monthly: pendulum.Duration = pendulum.duration(months=1)

# Inspect the next few clock emissions.
schedule: IntervalSchedule = IntervalSchedule(start_date=next_start_date, interval=monthly)
print(schedule.next(n=3))
# [
#   DateTime(2022, 1, 1, 8, 0, 0, tzinfo=Timezone('America/Los_Angeles')), 
#   DateTime(2022, 1, 31, 8, 0, 0, tzinfo=Timezone('America/Los_Angeles')), 
#   DateTime(2022, 3, 2, 8, 0, 0, tzinfo=Timezone('America/Los_Angeles'))
# ]

Why does the

IntervalSchedule

not fire on

2022-01-02

,

2022-02-02

,

2022-03-02

, etc? It appears to just be incrementing by 30 days, but that’s not quite what I’d expect. Is this a

pendulum

thing? (Edit: it’s maybe worth noting that in the example above, just doing

next_start_date + monthly

does give you the correct

DateTime(2022, 1, 2, 8, 0, 0, tzinfo=Timezone('America/Los_Angeles'))

. So I think it may actually be a Prefect thing?)

Using the good old cron, this would be:

import pendulum
from prefect.schedules import CronSchedule

schedule = CronSchedule("0 8 2 * *", start_date=pendulum.today(tz="America/Los_Angeles"))

for sched in schedule.next(20):
    print(sched)

but we also support RRule schedules, maybe it can be even easier for you

Yeah, I ended up pointing him to CronSchedule which works as expected. This just seems like a bug in the

IntervalScheduler

, so I was wondering if it was known. Would it be helpful to file an issue? I couldn’t find any existing issues referring to this situation 🤔 Regardless, thank you @Anna Geller!

this website is a life saver https://crontab.guru