Example of a class with a thread

thread_test.py

#!/usr/bin/env python

import threading
import time
import weakref

class BadRobot:

    def __init__(self):
        self.should_disconnect = False
        self.command_thread = threading.Thread(target=self.command_thread_func)
        print(f"Starting {self}")
        self.command_thread.start()

        self.latest_command = None

    def __del__(self):
        # NOTE: this will never be called :(
        print(f'deleting BadRobot {self}')
        self.should_disconnect = True

    def set_command(self, command):
        self.latest_command = command

    def command_thread_func(self):
        while True:
            print(f"{self} sending self.latest_command to motor controllers...")
            if self.should_disconnect:
                break
            time.sleep(0.1)


class Robot:

    def __init__(self):
        self.should_disconnect = False
        # NOTE: The trick is to use the pure function name Robot.threaded_func, which is not already bound to 'self'
        # and then to pass a weak ref to thread_func instead and
        self.command_thread = threading.Thread(target=Robot.command_thread_func, args=(weakref.proxy(self),))
        print(f"Starting {self}")
        self.command_thread.start()

        self.latest_command = None

    def __del__(self):
        print(f'deleting Robot {self}')
        self.should_disconnect = True

    def set_command(self, command):
        self.latest_command = command

    def command_thread_func(self):
        # NOTE: here self is a weakref, so Robot is eligable for garbage collection
        #  as even if this function is still running. Without the weak ref,
        #  Robot would be kept alive because this function still references 'self'
        try:
            while True:
                print(f"{self} sending self.latest_command to motor controllers...")
                if self.should_disconnect:
                    break
                time.sleep(0.1)
        except ReferenceError:
            pass

def main():
    # NOTE: this function creates "scope" for robot, which is necessary for this test
    robot = Robot()
    # NOTE: the following would never exit :(
    #robot = BadRobot()

if __name__ == '__main__':
    main()
    #print("ok, BadRobot should be dead now.... but it's not.")
    # NOTE: the following would never exit, because robot is never considered for garbage collection
    #robot = Robot()