Obstacle Avoiding Robot using Raspberry Pi

import RPi.GPIO as GPIO
import time

GPIO.setwarnings(False)
GPIO.setmode(GPIO.BCM)

TRIG = 17   #11
ECHO = 27   #13
statusLED = 22

pin1MotorA=16   #32
pin2MotorA=12   #36
pin1MotorB=21   #40
pin2MotorB=20   #38

GPIO.setup(TRIG,GPIO.OUT)
GPIO.setup(ECHO,GPIO.IN)
GPIO.setup(statusLED,GPIO.OUT)

GPIO.setup(pin1MotorA,GPIO.OUT)
GPIO.setup(pin2MotorA,GPIO.OUT)
GPIO.setup(pin1MotorB,GPIO.OUT)
GPIO.setup(pin2MotorB,GPIO.OUT)

GPIO.output(statusLED, 1)

time.sleep(5)

def stop():
    GPIO.output(pin1MotorA, 0)
    GPIO.output(pin2MotorA, 0)
    GPIO.output(pin1MotorB, 0)
    GPIO.output(pin2MotorB, 0)
    print "stop"

def forward():
    GPIO.output(pin1MotorA, 1)
    GPIO.output(pin2MotorA, 0)
    GPIO.output(pin1MotorB, 1)
    GPIO.output(pin2MotorB, 0)
    print "Forward"

def back():
    GPIO.output(pin1MotorA, 0)
    GPIO.output(pin2MotorA, 1)
    GPIO.output(pin1MotorB, 0)
    GPIO.output(pin2MotorB, 1)
    print "back"

def left():
    GPIO.output(pin1MotorA, 0)
    GPIO.output(pin2MotorA, 1)
    GPIO.output(pin1MotorB, 1)
    GPIO.output(pin2MotorB, 0)
    print "left"

def right():
    GPIO.output(pin1MotorA, 1)
    GPIO.output(pin2MotorA, 0)
    GPIO.output(pin1MotorB, 0)
    GPIO.output(pin2MotorB, 1)
    print "right"

stop()
count=0
while True:
 i=0
 avgDistance=0
 for i in range(5):
  GPIO.output(TRIG, False)
  time.sleep(0.1)

  GPIO.output(TRIG, True)
  time.sleep(0.00001)
  GPIO.output(TRIG, False)

  while GPIO.input(ECHO)==0:
       GPIO.output(statusLED, False)
  pulse_start = time.time()

  while GPIO.input(ECHO)==1:
       GPIO.output(statusLED, False)
  pulse_end = time.time()
  pulse_duration = pulse_end - pulse_start

  distance = pulse_duration * 17150
  distance = round(distance,2)
  avgDistance=avgDistance+distance

 #avgDistance=avgDistance/5
 print avgDistance
 flag=0
 if avgDistance < 15:      #Check whether the distance is within 15 cm range
    count=count+1
    stop()
    time.sleep(1)
    back()
    time.sleep(1.5)
    if (count%3 ==1) & (flag==0):
     right()
     flag=1
    else:
     left()
     flag=0
    time.sleep(1.5)
    stop()
    time.sleep(1)
 else:
    forward()
    flag=0