Stepper Motor key control

[cel]

Hello,
I'm writing a program to control a stepper motor using keyboard presses. The problem I'm having is that once I press a key to start the motor turning in one direction, I don't know how to interrupt the movement to either stop it or turn it in a different direction. I tried adding an if statement within one of the for loops but that did not work.

import curses
import time
import RPi.GPIO as GPIO

screen = curses.initscr()
curses.noecho() 
curses.cbreak()
screen.keypad(True)

GPIO.setmode(GPIO.BOARD)

ControlPin = [7,11,13,15]

for pin in ControlPin:
	GPIO.setup (pin, GPIO.OUT)
	GPIO.output (pin, 0)

seq2 = [[1,0,0,0],
	[1,0,0,0],
	[0,1,0,0],
	[0,1,0,0],
	[0,0,1,0],
	[0,0,1,0],
	[0,0,0,1],
	[0,0,0,1],
	[1,0,0,0],]

seq3 = [[1,0,0,0],
	[0,0,0,1],
	[0,0,0,1],
	[0,0,1,0],
	[0,0,1,0],
	[0,1,0,0],
	[0,1,0,0],
	[1,0,0,0],
	[1,0,0,0],]

try:
        while True:   
            char = screen.getch()
            if char == ord('q'):
                break
                        # right turning
            elif char == curses.KEY_RIGHT:
                for i in range(512):
                    print("right")
                    if char == curses.KEY_LEFT or char == 10:
                        break
                    for halfstep in range(9):
                        for pin in range(4):
                            GPIO.output(ControlPin[pin], seq2[halfstep][pin])
                        time.sleep(0.001)
                        
                        # left turning
            elif char == curses.KEY_LEFT:
                for i in range(512):
                    print("left")
                    if char == curses.KEY_RIGHT or char == 10:
                        break
                    for halfstep in range(9):
                        for pin in range(4):
                            GPIO.output(ControlPin[pin], seq3[halfstep][pin])
                        time.sleep(0.001)
                        
                        # stop
            elif char == 10:
                for i in range(512):
                    print("stop")
                    if char == curses.KEY_LEFT or char == curses.KEY_RIGHT:
                        break
                    for halfstep in range(9):
                        for pin in range(4):
                            GPIO.output(ControlPin[pin], seq2[halfstep][pin])
                        time.sleep(0.001)

        GPIO.cleanup()
except:
        GPIO.cleanup()
	print("error")