Let's review another example where we implement a simple daemon using OOP that turns on/off lights at specified times of the day. In order to be able to perform tasks at scheduled times, we will make use of the schedule library (https://github.com/dbader/schedule). It could be installed as follows:

    sudo pip3 install schedule

Let's call our class, LightScheduler. It should be capable of accepting start and top times to turn on/off lights at given times. It should also provide override capabilities to let the user turn on/off lights as necessary. Let's assume that the light is controlled using PowerSwitch Tail II (http://www.powerswitchtail.com/Pages/default.aspx). It is interfaced as follows:

The following is the LightSchedular class created:

class LightScheduler(object): 
    """A Python class to turn on/off lights""" 

    def __init__(self, start_time, stop_time): 
        self.start_time = start_time 
        self.stop_time = stop_time 
        # lamp is connected to GPIO pin2.
        self.lights = OutputDevice(2)

Whenever an instance of LightScheduler is created, the GPIO pin is initialized to control the PowerSwitch Tail II. Now, let's add methods to turn on/off lights:

def init_schedule(self): 
        # set the schedule 
        schedule.every().day.at(self.start_time).do(self.on) 
        schedule.every().day.at(self.stop_time).do(self.off) 

    def on(self): 
        """turn on lights""" 
        self.lights.on() 

    def off(self): 
        """turn off lights""" 
        self.lights.off()

In the init_schedule() method, the start and stop times that were passed as arguments are used to initialize schedule to turn on/off the lights at the specified times.

Put it together, we have:

import schedule 
import time 
from gpiozero import OutputDevice 

class LightScheduler(object): 
    """A Python class to turn on/off lights""" 

    def __init__(self, start_time, stop_time): 
        self.start_time = start_time 
        self.stop_time = stop_time 
        # lamp is connected to GPIO pin2.
        self.lights = OutputDevice(2) 

    def init_schedule(self): 
        # set the schedule 
        schedule.every().day.at(self.start_time).do(self.on) 
        schedule.every().day.at(self.stop_time).do(self.off) 

    def on(self): 
        """turn on lights""" 
        self.lights.on() 

    def off(self): 
        """turn off lights""" 
        self.lights.off() 


if __name__ == "__main__": 
    lamp = LightScheduler("18:30", "9:30") 
    lamp.on() 
    time.sleep(50) 
    lamp.off() 
    lamp.init_schedule() 
    while True:
        schedule.run_pending() 
        time.sleep(1)

In the preceding example, the lights are scheduled to be turned on at 6:30 p.m. and turned off at 9:30 a.m. Once the jobs are scheduled, the program enters an infinite loop where it awaits task execution. This example could be run as a daemon by executing the file at start-up (add a line called light_scheduler.py to /etc/rc.local). After scheduling the job, it will continue to run as a daemon in the background.