切换键运行线程然后再次按下时停止线程？

Question

I'm currently working on a program and setup a toggle key that starts a thread when it's first clicked, and I want it to stop the thread when the key is pressed again. Currently I've tried this piece of code, but it came out with an error.

def on_press(key):
    try: k = key.char
    except: k = key.name
    if key == (KeyCode(char='e')):
        print("Key Pressed")
        clicker = threading.Thread(target=run)
        if running == False:
            print("Starting")
            clicker.start()
        else:
            print("Stopping")
            clicker.join()

lis = keyboard.Listener(on_press=on_press)
lis.start() # start to listen on a separate thread
lis.join() # no this if main thread is polling self.keys

The error I get is:

raise RuntimeError("cannot join thread before it is started")
  RuntimeError: cannot join thread before it is started**

Answer 1

You should check what you have in variable running - ie. print(running) - because it decides when to execute code in if/else and it runs click.join() directly after creating Thread before you run clicker.start()`

As for me you should create therad inside if running == False

You should also use global to assing values to external variable - now you create local clicker which will be removed when it exits on_press and you will not have access to this thread. You should also change value running when you started thead`

---

BTW:

For True/False you should rather use is instead of ==

You can also use more readable if not running instead of if running is False:

---

I didn't test it

# from ... import ...

# --- functions ---

def on_press(key):
    global running   # inform function that it has to assign value to external variable 
    global clicker
    
    try:    # PEP8: don't put it in one line - it make code unreadable for human 
        k = key.char
    except: 
        k = key.name
        
    if key == KeyCode(char='e'):
        print("Key Pressed")
        
        if not running: # the same as `if running == False:` 
            print("Starting")
            clicker = threading.Thread(target=run)
            clicker.start()
            running = True
        else:
            print("Stopping")
            clicker.join()
            running = False

# --- main ---

running = False  # default value at start

lis = keyboard.Listener(on_press=on_press)
lis.start()
lis.join()

---

if you don't use running in other places in code then you could use clicker = None to control if thread is running.

# from ... import ...

# --- functions ---

def on_press(key):
    global clicker   # inform function that it has to assign value to external variable 
    
    try:    # PEP8: don't put it in one line - it make code unreadable for human 
        k = key.char
    except: 
        k = key.name
        
    if key == KeyCode(char='e'):
        print("Key Pressed")
        
        if not clicker:
            print("Starting")
            clicker = threading.Thread(target=run)
            clicker.start()
        else:
            print("Stopping")
            clicker.join()
            clicker = None

# --- main ---

clicker = None  # default value at start

lis = keyboard.Listener(on_press=on_press)
lis.start()
lis.join()

---

BTW:

If thread is running then join() waits for its end - but it doesn't kill it so you may wait forever.

You should use value running also inside run() to stop it.

def run():

    while running:
        #... code ...

or

def run():

    while True:
        #... code ...
   
        if not running:
             return

        #... code ...

and then you have to set running before start() and join()

    if not running:
        print("Starting")
        clicker = threading.Thread(target=run)
        running = True  # it has to be before `start()` 
        clicker.start()
    else:
        print("Stopping")
        running = False  # it has to be before `join()` 
        clicker.join()

---

EDIT:

Minimal working code - I tested it.

from pynput import keyboard
import datetime
import time
import threading

# --- functions ---

def run():

    print('Running thread')
    while running:
        print(datetime.datetime.now())
        time.sleep(1)
    print('Exiting thread')

def on_press(key):
    global running   # inform function that it has to assign value to external variable
    global clicker

    try:    # PEP8: don't put it in one line - it make code unreadable for human
        k = key.char
    except:
        k = key.name

    if key == keyboard.KeyCode(char='e'):
        print("Key Pressed")

        if not running: # the same as `if running == False:`
            print("Starting thread")
            clicker = threading.Thread(target=run)
            running = True  # it has to be before `start()`
            clicker.start()
        else:
            print("Stopping thread")
            running = False  # it has to be before `join()`
            clicker.join()

    # press `q` to exit
    if key == keyboard.KeyCode(char='q'):
        return False

# --- main ---

running = False  # default value at start

try:
    print("Starting program")
    print("- press E to start/stop thread")
    print("- press Q to exit")
    print("- press Ctrl+C to exit")
    
    lis = keyboard.Listener(on_press=on_press)
    lis.start()
    print("Listening ...")
    
    lis.join()
    print("Exiting program")
except KeyboardInterrupt:
    print("Stoped by Ctrl+C")
else:
    print("Stoped by Q")
finally:
    if running:
        running = False
        clicker.join()

Answer 2

If the key pressed is the same as the start_stop_key, stop clicking if the running flag is set to true in the thread otherwise start it. If the key pressed is the exit key, call the exit method in the thread and stop the listener

start_stop_key = KeyCode(char='s')
exit_key = KeyCode(char='e')
...............
def on_press(key):
if key == start_stop_key:
    if click_thread.running:
        click_thread.stop_clicking()
    else:
        click_thread.start_clicking()
elif key == exit_key:
    click_thread.exit()
    listener.stop()