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Crontabs


NOTE: I've recently discovered the Rocketry and Huey projects, which you should probably use instead of crontabs. They are just better than crontabs.


Think of crontabs as a quick-and-dirty solution you can throw into one-off python scripts to execute tasks on a cron-like schedule.

Crontabs is a small pure-python library that was inspired by the excellent schedule library for python.

In addition to having a slightly different API, crontabs differs from the schedule module in the following ways.

Why Crontabs

Python has no shortage of cron-like job scheduling libraries, so why create yet another. The honest answer is that I couldn't find one that met a simple list of criteria.

Installation

pip install crontabs

Usage

Schedule a single job

from crontabs import Cron, Tab
from datetime import datetime


def my_job(*args, **kwargs):
    print('args={} kwargs={} running at {}'.format(args, kwargs, datetime.now()))


# Will run with a 5 second interval synced to the top of the minute
Cron().schedule(
    Tab(name='run_my_job').every(seconds=5).run(my_job, 'my_arg', my_kwarg='hello')
).go()

Schedule multiple jobs

from crontabs import Cron, Tab
from datetime import datetime


def my_job(*args, **kwargs):
    print('args={} kwargs={} running at {}'.format(args, kwargs, datetime.now()))


# All logging messages are sent to sdtout
Cron().schedule(
    # Turn off logging for job that runs every five seconds
    Tab(name='my_fast_job', verbose=False).every(seconds=5).run(my_job, 'fast', seconds=5),

    # Go ahead and let this job emit logging messages
    Tab(name='my_slow_job').every(seconds=20).run(my_job, 'slow', seconds=20),
).go()

Schedule future job to run repeatedly for a fixed amount of time

from crontabs import Cron, Tab
from datetime import datetime


def my_job(*args, **kwargs):
    print('args={} kwargs={} running at {}'.format(args, kwargs, datetime.now()))


Cron().schedule(
    Tab(
        name='future_job'
    ).every(
        seconds=5
    ).starting(
        '12/27/2017 16:45'  # This argument can either be parsable text or datetime object.
    ).run(
        my_job, 'fast', seconds=5
    )
# max_seconds starts from the moment go is called.  Pad for future run times accordingly.
).go(max_seconds=60)

Cron API

The Cron class has a very small api

methodDescription
.schedule()[Required] Specify the different jobs you want using Tab instances
.go()[Required] Start the crontab manager to run all specified tasks
.get_logger()A class method you can use to get an instance of the crontab logger

Tab API with examples

The api for the Tab class is designed to be composable and readable in plain English. It supports the following "verbs" by invoking methods.

methodDescription
.run()[Required] Specify the function to run.
.every()[Required] Specify the interval between function calls.
.starting()[Optional] Specify an explicit time for the function calls to begin.
.lasting()[Optional] Specify how long the task will continue being iterated.
.until()[Optional] Specify an explicit time past which the iteration will stop
.during()[Optional] Specify time conditions under which the function will run
.excluding()[Optional] Specify time conditions under which the function will be inhibited

Run a job indefinitely

from crontabs import Cron, Tab
from datetime import datetime


def my_job(name):
    print('Running function with name={}'.format(name))


Cron().schedule(
    Tab(name='forever').every(seconds=5).run(my_job, 'my_func'),
).go()

Run one job indefinitely, another for thirty seconds, and another until 1/1/2030

from crontabs import Cron, Tab
from datetime import datetime


def my_job(name):
    print('Running function with name={}'.format(name))


Cron().schedule(
    Tab(name='forever').run(my_job, 'forever_job').every(seconds=5),
    Tab(name='for_thirty').run(my_job, 'mortal_job').every(seconds=5).lasting(seconds=30),
    Tab(name='real_long').run(my_job, 'long_job').every(seconds=5).until('1/1/2030'),
).go()

Run job every half hour from 9AM to 5PM excluding weekends

from crontabs import Cron, Tab
from datetime import datetime

def my_job(name):
    # Grab an instance of the crontab logger and write to it.
    logger = Cron.get_logger()
    logger.info('Running function with name={}'.format(name))


def business_hours(timestamp):
    return 9 <= timestamp.hour < 17

def weekends(timestamp):
    return timestamp.weekday() > 4


# Run a job every 30 minutes during weekdays.  Stop crontabs after it has been running for a year.
# This will indiscriminately kill every Tab it owns at that time.
Cron().schedule(
    Tab(
        name='my_job'
    ).run(
        my_job, 'my_job'
    ).every(
        minutes=30
    ).during(
        business_hours
    ).excluding(
        weekends
    )
).go(max_seconds=3600 * 24 * 365)

Run test suite with

git clone git@github.com:robdmc/crontabs.git
cd crontabs
pip install -e .[dev]
py.test -s -n 8   # Might need to change the -n amount to pass

Projects by robdmc.