CronTask

Last updated: 18 Jul 2024

You can write a handler that subclasses CronTask to execute code on a schedule. You might use this to automate reporting on task performance (every hour, send the number of tasks created during the previous hour, and the number of tasks completed during the previous hour), to send birthday wishes to your patients (at 7am every morning, find patients born on this day and send them an email wishing them a happy birthday), or to send customized appointment reminders (every hour, find appointments that start on this hour the following day and send the patients of those appointments a message that says “Dr. X is looking forward to seeing you at (location) at (time)”).

Example #

This example CronTask shows an extremely basic example that just logs the time. You can see the critical pieces here:

• Subclass CronTask
• Set your SCHEDULE with a cron string
• Implement an execute method with the code you want to schedule to run, returning a list containing any effects you want to return, or an empty list if you do not wish to return any effects.

from canvas_sdk.handlers.cron_task import CronTask
from canvas_sdk.effects import Effect

from logger import log


class LogTheTime(CronTask):
    # A cron string.
    #           ┌───────────── minute (0 - 59)
    #           │ ┌───────────── hour (0 - 23)
    #           │ │ ┌───────────── day of the month (1 - 31)
    #           │ │ │ ┌───────────── month (1 - 12)
    #           │ │ │ │ ┌───────────── day of the week (0 - 6) (Sunday to Saturday)
    #           │ │ │ │ │
    #           │ │ │ │ │
    #           │ │ │ │ │
    SCHEDULE = "* * * * *"  # Run every minute, which is the most frequently something can run.

    def execute(self) -> list[Effect]:
        # The current timestamp can be found as an iso8601 string in
        # `self.target`
        log.info(f"The current time is {self.target}")

        # We don't need to return any effects
        return []

Output #

Here’s what this scheduled task would output in the logs:

INFO 2024-07-18 18:47:00,000 The current time is 2024-07-18T18:47:00.000000+00:00