ischedule 0.91

Open source, single-thread interval scheduler

An elegant and simple way to schedule periodic tasks in Python. Created because schedule is too complicated and counterintuitively does not account for the time it takes for the job function to execute.

Implementational details

• Both the scheduler and the task run in the main thread. No new threads are created.
• Each task can run until it finishes.
• Each execution of run_pending checks the tasks in the same order as they were added by schedule. It executes the first task that is ready to be executed.* If a task was not executed during the scheduled interval, a single execution will be missed
• A task execution will be skipped if a the next execution of the same task is due by the time the control is returned to the scheduler.
• Exceptions during the execution are propagated out of run_pending, and can be dealth with by the caller.

Example

import time

from src.ischedule.ischedule import schedule, run_loop
from threading import Event

start_time = time.time()
stop_event = Event()


def job_1():
    dt = time.time() - start_time
    print(f"Started a _fast_ job at t={dt:.2f}")
    if dt > 3:
        stop_event.set()


def job_2():
    dt = time.time() - start_time
    if dt > 2:
        return
    print(f"Started a *slow* job at t={dt:.2f}")
    time.sleep(1)


schedule(job_1, interval=0.1)
schedule(job_2, interval=0.5)

run_loop(stop_event=stop_event)

This example produces the following output:

Started a _fast_ job at t=0.10
Started a _fast_ job at t=0.20
Started a _fast_ job at t=0.31
Started a _fast_ job at t=0.41
Started a _fast_ job at t=0.50
Started a *slow* job at t=0.50
Started a _fast_ job at t=1.51
Started a *slow* job at t=1.51
Started a _fast_ job at t=2.52
Started a _fast_ job at t=2.61
Started a _fast_ job at t=2.71
Started a _fast_ job at t=2.81
Started a _fast_ job at t=2.90
Started a _fast_ job at t=3.00

The fast job runs every 0.1 seconds, and completes quickly. When the slow job starts running at t=0.5, it doesn't return control until one second later, at t=1.50s. By that time, both the fast and the slow job become pending, and are executed in the order they were added to the scheduler. The slow job does not run after t=2.0, so the fast job returns to running normally every 0.1 seconds.