Check value change within class without setter in Python?

Question

Every 15 seconds, or when the potato color changes, I want to print potato.color.

How can I monitor the potato color changes event without a setter function?

There is a way to do this with an Observer pattern How to trigger function on value change?

which uses a setter and a mysterious callback.

Now, from the potato color setter set_color, I could call the event_publisher everytime. The problem is, that the potato.color is usually just set with potato.color = "poison-green", and I can't prevent people from setting the color that way.

Now what this code does:

• Potato.set_color is never called, because the programmer was silly. But could be used for the observer_pattern, and everytime the value is set again, we call event_publisher. Problem: The programmer was silly, and is unused.

• frequency_publisher prints every 15 seconds

• event_publisher is supposed to monitor the own class, and call the event_publisher whenever the self.color changes. My favorite solution, because refactoring the code to call set_color is difficult.

Is there a way to write either the event_publisher outside the function, or the my_color_changed_event function?

import asyncio
import random

class Potato:
    color = "potato-yellow"

    def set_color(self, color_):
        # Is there a way around this?
        # Someone could just set potato.color = "green" without calling this setter
        self.color = color_
        event_publisher(self)

    async def my_color_changed_event(self):

        while True:
            if random.randint(1, 100) < 30:  # PLACEHOLDER FOR if self.color changed???
                await asyncio.sleep(5)
                return True
            return False

async def frequency_publisher(potato_):
    while True:
        print("Publish by time!", potato_.color)
        await asyncio.sleep(15)


async def event_publisher(potato_):
    while True:
        # Somehow watch potato_ for changes
        # ???

        event_ = await potato_.my_color_changed_event(potato_)
        if event_:
            print("Publish by event!", potato_.color)


if __name__ == '__main__':
    potato = Potato
    while True:
        try:
            loop = asyncio.get_event_loop()
            loop.run_until_complete(asyncio.gather(
                event_publisher(potato),
                frequency_publisher(potato)
            ))

        except KeyboardInterrupt:
            break