(Python help) Change in logic not breaking 'while' loop?

[btcg2807]

Hello, I am currently a beginner at Python coding thus I apologise if there is a basic/obvious solution to this. I want to code a program that runs 2 motors forwards simultaneously for 3 seconds, then backwards for 3 seconds. In addition, I've added a photoelectric sensor (WT160-F172) that will act as a collision detector for the motors. I can only get the sensor to stop the motors and continue running forwards (how i want it to work) when the loop is infinite (no time.sleep) . When i make it the finite loop i want (3 seconds front and 3 second back), i do not know how to get the sensor to function during the loop, the sensor only affects the motors between two said finite loops. I'm on python 3 and raspberry pi 3.

import RPi.GPIO as GPIO
import time

GPIO.setmode(GPIO.BOARD)
GPIO.setup(7,GPIO.IN, pull_up_down=GPIO.PUD_DOWN)
GPIO.setup(11,GPIO.OUT)
GPIO.setup(12,GPIO.OUT)
GPIO.setup(13,GPIO.OUT)
GPIO.setup(15,GPIO.OUT)

try:
	while True:
		print("Sensor Value:")
		value = GPIO.input(7)
		print(value)
		if (value == 0):
			print("Move forward")
			GPIO.output(11,False)
			GPIO.output(12,True)
			GPIO.output(13,True)
			GPIO.output(15,False)
			time.sleep(3)
			print("Move backward")
			GPIO.output(11,True)
			GPIO.output(12,False)
			GPIO.output(13,False)
			GPIO.output(15,True)
			time.sleep(3)
		elif (value == 1):
			print("Obstacle detected")
			GPIO.output(11,False)
			GPIO.output(12,False)
			GPIO.output(13,False)
			GPIO.output(15,False)
except KeyboardInterrupt:
	pass
finally:
	GPIO.cleanup()

There is evidently a wrong usage of the loop functions in this code thus any help would be appreciated.

[Larz60+]

Better way (untested):

import RPi.GPIO as GPIO
import time

def init():
    GPIO.setmode(GPIO.BOARD)
    GPIO.setup(7,GPIO.IN, pull_up_down=GPIO.PUD_DOWN)
    GPIO.setup(11,GPIO.OUT)
    GPIO.setup(12,GPIO.OUT)
    GPIO.setup(13,GPIO.OUT)
    GPIO.setup(15,GPIO.OUT)

def move_forward():
    print("Move forward")
    GPIO.output(11,False)
    GPIO.output(12,True)
    GPIO.output(13,True)
    GPIO.output(15,False)
    time.sleep(3)

def move_backward():
    GPIO.output(11,True)
    GPIO.output(12,False)
    GPIO.output(13,False)
    GPIO.output(15,True)
    time.sleep(3)

def start()
    init()
    try:
        while True:
            move_forward()
            move_backward()
    except KeyboardInterrupt:
        pass
    finally:
        GPIO.cleanup()