i2c_outputs.py

import smbus
import time

#bus = smbus.SMBus(0)  # Rev 1 Pi uses 0
bus = smbus.SMBus(1) # Rev 2 Pi uses 1

DEVICE = 0x20 # Device address (A0-A2)
IODIRA = 0x00 # Pin direction register
OLATA  = 0x15 # Register for outputs
GPIOA  = 0x13 # Register for inputs

# Set all GPA pins as outputs by setting
# all bits of IODIRA register to 0
bus.write_byte_data(DEVICE,IODIRA,0x00)

# Set output all 7 output bits to 0
bus.write_byte_data(DEVICE,OLATA,0)

for MyData in range(0,8):
  # Count from 1 to 8 which in binary will count 
  # from 001 to 111
  bus.write_byte_data(DEVICE,OLATA,MyData)
  print MyData
  time.sleep(3)
  
# Set all bits to zero
bus.write_byte_data(DEVICE,OLATA,0)