cannot stop a thread in Python, using Event Objects, thread as separate module

Question

I am playing with a threading test code derived from here (or here) but I can't figure what do I miss in my test code. I am running the thread in a separate file, if this makes any difference (?).

The thread starts ok, but when trying to stop it gives "'Thread' object has no attribute 'stopit'" error.

Main test code is this:

#!/usr/bin/env python

import os
import sys
import threading
import time

import test_thread_external as TestThreadExternal

# ---

class test(object):
    def __init__(self):
        pass

    def main(self):
        print ("starting thread")
        test_th = threading.Thread(target = TestThreadExternal.stoppable, args = ())
        test_th.start()
        time.sleep(3)
        print ("stopping thread")
        self.error_flag = False
        try:
            test_th.stopit()
        except Exception as e:
            self.error_flag = True
            self.err = str(e)
        if not self.error_flag:
            time.sleep(3)
            print ("exit supposedly with thread stopped")  # can be checked with is_alive()
        else:
            print ("exit with error %s" % (self.err))

# ---

if __name__ == '__main__':
    try:
        app = test()
        app.main()
    except KeyboardInterrupt:
        print ("exit via Ctrl+C")
    finally:
        try:
            sys.exit(0)
        except SystemExit:
            os._exit(0)

and the thread itself is this one, stored in file 'test_thread_external.py':

#!/usr/bin/env python

import threading
import time

# ---

class stoppable(threading.Thread):
    def __init__(self):
        super(stoppable, self).__init__()
        self._stopper = threading.Event()
        while True:
            print ("thread running")
            if self.stopped():
                break
            time.sleep(1)
        print ("thread on the way to its exit")

    def stopit(self):
        self._stopper.set()

    def stopped(self):
        return self._stopper.is_set()

What do I do wrong ?

Small later edit: changed _stop with _stopper in order to avoid "'Event' object is not callable" error in case using join() (not shown here) -- as explained in this answer to a former question.

Answer 1

When you create a thread, target is the function to run in the thread.

You're creating a threading.Thread and passing stoppable (which is a subclass of Thread) as target.

From your description, it seems to me you actually need to create an instance of type stoppable (without passing target). That type should only do initializations in its __init__, and the code which should run in the thread should be in its run method:

class stoppable(threading.Thread):
    def __init__(self):
        super(stoppable, self).__init__()
        self._stop = threading.Event()

    def run(self):    
        while True:
            print ("thread running")
            if self.stopped():
                break
            time.sleep(1)
        print ("thread on the way to its exit")

    ...

And:

test_th = TestThreadExternal.stoppable()