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crontab

Parse and use crontab schedules in Python

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Copyright 2011-2021 Josiah Carlson

Released under the LGPL license version 2.1 and version 3 (you can choose which you'd like to be bound under).

Description

This package intends to offer a method of parsing crontab schedule entries and determining when an item should next be run. More specifically, it calculates a delay in seconds from when the .next() method is called to when the item should next be executed.

Comparing the below chart to http://en.wikipedia.org/wiki/Cron#CRON_expression you will note that W and # symbols are not supported.

============= =========== ================= ============== =========================== Field Name Mandatory Allowed Values Default Value Allowed Special Characters ============= =========== ================= ============== =========================== Seconds No 0-59 0 * / , - Minutes Yes 0-59 N/A * / , - Hours Yes 0-23 N/A * / , - Day of month Yes 1-31 N/A * / , - ? L Month Yes 1-12 or JAN-DEC N/A * / , - Day of week Yes 0-6 or SUN-SAT N/A * / , - ? L Year No 1970-2099 * * / , - ============= =========== ================= ============== ===========================

If your cron entry has 5 values, minutes-day of week are used, default seconds is and default year is appended. If your cron entry has 6 values, minutes-year are used, and default seconds are prepended.

As such, only 5-7 value crontab entries are accepted (and mangled to 7 values, as necessary).

Sample individual crontab fields

Examples of supported entries are as follows::

*
*/5
7/8
3-25/7
3,7,9
0-10,30-40/5

For month or day of week entries, 3 letter abbreviations of the month or day can be used to the left of any optional / where a number could be used.

For days of the week::

For month::

Installation

::

pip install crontab

Example uses

::

>>> from crontab import CronTab
>>> from datetime import datetime
>>> # define the crontab for 25 minutes past the hour every hour
... entry = CronTab('25 * * * *')
>>> # find the delay from when this was run (around 11:13AM)
... entry.next()
720.81637899999998
>>> # find the delay from when it was last scheduled
... entry.next(datetime(2011, 7, 17, 11, 25))
3600.0

Notes

At most one of 'day of week' or 'day of month' can be a value other than '?' or ''. We violate spec here and allow '' to be an alias for '?', in the case where one of those values is specified (seeing as some platforms don't support '?').

This module also supports the convenient aliases::

@yearly
@annually
@monthly
@weekly
@daily
@hourly

Example full crontab entries and their meanings::

30 */2 * * * -> 30 minutes past the hour every 2 hours
15,45 23 * * * -> 11:15PM and 11:45PM every day
0 1 ? * SUN -> 1AM every Sunday
0 1 * * SUN -> 1AM every Sunday (same as above)
0 0 1 jan/2 * 2011-2013 ->
    midnight on January 1, 2011 and the first of every odd month until
    the end of 2013
24 7 L * * -> 7:24 AM on the last day of every month
24 7 * * L5 -> 7:24 AM on the last friday of every month
24 7 * * Lwed-fri ->
    7:24 AM on the last wednesday, thursday, and friday of every month

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