Endless loop at the touch of a button

Question

I need to start endless loop by pressing Space (for example) and end it pressing Space again

@win.event
def on_draw():
    (some code of drawing)


@win.event
def on_key_press(symbol, modifiers):
    global x,y,z,t
    elif symbol == key.SPACE:
        t += 0.05
        x = ((1 - t) ** 3) * (-180) + 3 * t * ((1 - t) ** 2) * (100) + 3 * (t ** 2) * (1 - t) * (0) + (t ** 3) * (200)
        y = ((1 - t) ** 3) * 70 + 3 * t * ((1 - t) ** 2) * (140) + 3 * (t ** 2) * (1 - t) * (140) + (t ** 3) * (
        70)
        z = ((1 - t) ** 3) * 0 + 3 * t * ((1 - t) ** 2) * (100) + 3 * (t ** 2) * (1 - t) * (100) + (t ** 3) * (
        0)
        (here should be a function of endless moving (drawing) while Space haven't pressed again)

Answer 1

This is not the right choice to do it. You already have a loop, the game loop. Use it!

Create 2 state variables start_loop and run_loop:

start_loop = False
run_loop = False

If space is pressed then you've to decide what to do.
If the loop is not running (not run_loop), then start the loop by setting start_loop = True. If the loop is running, then stop the loop by run_loop = False.

def on_key_press(symbol, modifiers):

    if symbol == key.SPACE:
        if not run_loop:
            start_loop = True
        else:
            run_loop = False

In the main loop you can have to distinguish 3 cased.

1. start_loop is True. Do the initializations and set the states to run the loop in the next frame (start_loop = False, run_loop = True)
2. run_loop is True. Do the code in the loop
3. default case, which does some drawing

def on_draw():

    global x,y,z,t

    if start_loop:
        start_loop = False
        run_loop = True

        t += 0.05
        x = ((1 - t) ** 3) * (-180) + 3 * t * ((1 - t) ** 2) * (100) + 3 * (t ** 2) * (1 - t) * (0) + (t ** 3) * (200)
        y = ((1 - t) ** 3) * 70 + 3 * t * ((1 - t) ** 2) * (140) + 3 * (t ** 2) * (1 - t) * (140) + (t ** 3) * (70)
        z = ((1 - t) ** 3) * 0 + 3 * t * ((1 - t) ** 2) * (100) + 3 * (t ** 2) * (1 - t) * (100) + (t ** 3) * (0)

    elif run_loop:

        # this is the loop
        # [...] (here should be a function of endless moving (drawing) while Space haven't pressed again)
        pass

    else:

        # this is default
        # [...] (some code of drawing)

---

Of course you've to add a schedule function by [schedule_interval], which runs the loop in an specified interval.

def run_loop(dt):
    on_draw()

pyglet.clock.schedule_interval(run_loop, 0.1) # run every tenth of a second
pyglet.app.run()