How to use Queue in threading

display_manager.py

from queue import Queue, PriorityQueue
from threading import Thread


class DisplayManager(Thread):

    def __init__(self, observer):
        Thread.__init__(self)
        self.queue = Queue()
        observer.subscribe(self.queue.put)

    def run(self):
        while True:
            change = self.queue.get()
            print("run change => ", change)
            print("queue size => ", self.queue.qsize())

display_observer.py

class DisplayObservable:

    listeners = []

    def __init__(self):
        pass

    def __new__(self):
        if not hasattr(self, 'instance'):
            self.instance = super(DisplayObservable, self).__new__(self)
        return self.instance

    def subscribe(self, listener):
        self.listeners.append(listener)

    def onNotify(self, change):
        for listener in self.listeners:
            listener(change)

main.py

from display_observer import DisplayObservable
from display_manager import DisplayManager

if __name__ == '__main__':

    do = DisplayObservable()

    dm = DisplayManager(do)
    dm.start()

    print("Object created ", do)
    print("listener len ", len(do.listeners))

    do.onNotify("test data 1")

    do1 = DisplayObservable()
    print("Object created ", do1)
    print("listener len ", len(do1.listeners))

    do1.onNotify("test data 2")

    do2 = DisplayObservable()
    print("Object created ", do2)
    print("listener len ", len(do2.listeners))

    do2.onNotify("test data 3")