APScheduler API -- apscheduler.triggers.cron

apscheduler.triggers.cron

API

Trigger alias for add_job(): cron

class apscheduler.triggers.cron.CronTrigger(year=None, month=None, day=None, week=None, day_of_week=None, hour=None, minute=None, second=None, start_date=None, end_date=None, timezone=None)

Bases: apscheduler.triggers.base.BaseTrigger

Triggers when current time matches all specified time constraints, similarly to how the UNIX cron scheduler works.

Parameters:

year (int|str) – 4-digit year month (int|str) – month (1-12) day (int|str) – day of the (1-31) week (int|str) – ISO week (1-53) day_of_week (int|str) – number or name of weekday (0-6 or mon,tue,wed,thu,fri,sat,sun) hour (int|str) – hour (0-23) minute (int|str) – minute (0-59) second (int|str) – second (0-59) start_date (datetime|str) – earliest possible date/time to trigger on (inclusive) end_date (datetime|str) – latest possible date/time to trigger on (inclusive) timezone (datetime.tzinfo|str) – time zone to use for the date/time calculations (defaults to scheduler timezone)

Note

The first weekday is always monday.

Introduction

This is the most powerful of the built-in triggers in APScheduler. You can specify a variety of different expressions on each field, and when determining the next execution time, it finds the earliest possible time that satisfies the conditions in every field. This behavior resembles the “Cron” utility found in most UNIX-like operating systems.

You can also specify the starting date and ending dates for the cron-style schedule through the start_date and end_date parameters, respectively. They can be given as a date/datetime object or text (in the ISO 8601 format).

Unlike with crontab expressions, you can omit fields that you don’t need. Fields greater than the least significant explicitly defined field default to * while lesser fields default to their minimum values except for week and day_of_week which default to *. For example, day=1, minute=20 is equivalent to year='*', month='*', day=1, week='*', day_of_week='*', hour='*', minute=20, second=0. The job will then execute on the first day of every month on every year at 20 minutes of every hour. The code examples below should further illustrate this behavior.

Note

The behavior for omitted fields was changed in APScheduler 2.0. Omitted fields previously always defaulted to *.

Expression types

The following table lists all the available expressions for use in the fields from year to second. Multiple expression can be given in a single field, separated by commas.

Expression	Field	Description
*	any	Fire on every value
*/a	any	Fire every a values, starting from the minimum
a-b	any	Fire on any value within the a-b range (a must be smaller than b)
a-b/c	any	Fire every c values within the a-b range
xth y	day	Fire on the x -th occurrence of weekday y within the month
last x	day	Fire on the last occurrence of weekday x within the month
last	day	Fire on the last day within the month
x,y,z	any	Fire on any matching expression; can combine any number of any of the above expressions

Daylight saving time behavior

The cron trigger works with the so-called “wall clock” time. Thus, if the selected time zone observes DST (daylight saving time), you should be aware that it may cause unexpected behavior with the cron trigger when entering or leaving DST. When switching from standard time to daylight saving time, clocks are moved either one hour or half an hour forward, depending on the time zone. Likewise, when switching back to standard time, clocks are moved one hour or half an hour backward. This will cause some time periods to either not exist at all, or be repeated. If your schedule would have the job executed on either one of these periods, it may execute more often or less often than expected. This is not a bug. If you wish to avoid this, either use a timezone that does not observe DST, for instance UTC. Alternatively, just find out about the DST switch times and avoid them in your scheduling.

For example, the following schedule may be problematic:

# In the Europe/Helsinki timezone, this will not execute at all on the last sunday morning of March
# Likewise, it will execute twice on the last sunday morning of October
sched.add_job(job_function, 'cron', hour=3, minute=30)

Examples

from apscheduler.scheduler import BlockingScheduler

def job_function():
    print "Hello World"

sched = BlockingScheduler()

# Schedules job_function to be run on the third Friday
# of June, July, August, November and December at 00:00, 01:00, 02:00 and 03:00
sched.add_job(job_function, 'cron', month='6-8,11-12', day='3rd fri', hour='0-3')

sched.start()

You can use start_date and end_date to limit the total time in which the schedule runs:

# Runs from Monday to Friday at 5:30 (am) until 2014-05-30 00:00:00
sched.add_job(job_function, 'cron', day_of_week='mon-fri', hour=5, minute=30, end_date='2014-05-30')

The scheduled_job() decorator works nicely too:

@sched.scheduled_job('cron', id='my_job_id', day='last sun')
def some_decorated_task():
    print("I am printed at 00:00:00 on the last Sunday of every month!")

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