Make A File For The Script:

nano 8channel.py

#!/usr/bin/python
import RPi.GPIO as GPIO
import time

GPIO.setmode(GPIO.BCM)

# GPIO | Relay
#*************
#*************
# 13     01
# 19     02
# 20     03
# 21     04
# 22     05
# 23     06
# 26     07
# 27     08

# Initiate List With Pin GPIO Pin Numbers

gpioList = [13, 19, 20, 21, 22, 23, 26, 27]  #Update GPIO To What Is Being Used

for i in gpioList:
    GPIO.setup(i, GPIO.OUT)
    GPIO.output(i, GPIO.HIGH)

# Sleep Time Variables

sleepTimeShort = 0.2  #Change Time
sleepTimeLong = 0.1   #Change Time

# MAIN LOOP *****
# ***************

try:
    while True:
        for i in gpioList:
            GPIO.output(i, GPIO.LOW)
            time.sleep(sleepTimeShort);
            GPIO.output(i, GPIO.HIGH)
            time.sleep(sleepTimeLong);


# End Program Cleanly With Keyboard
except KeyboardInterrupt:
    print " Quit"

    # Reset GPIO Settings

    GPIO.cleanup()

To Run The Script:

python 8channel.py