Keyboard events of python+selenium

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This is python+selenium Keyboard events

#coding=utf-8
from selenium import webdriver
from selenium.webdriver.common.keys import Keys
# Import keys modular 
import time
driver = webdriver.Firefox()
driver.get('http://www.baidu.com')
driver.find_element_by_id("kw").send_keys("selenium+")
driver.find_element_by_id("kw").send_keys(Keys.BACK_SPACE)
# Delete the plus sign 
driver.find_element_by_id("kw").send_keys(Keys.SPACE)
# Enter a space 
driver.find_element_by_id("kw").send_keys(u" course ")
# Import tutorial 
driver.find_element_by_id("kw").send_keys(Keys.CONTROL,'a')
time.sleep(2)
#ctrl+a
driver.find_element_by_id("kw").send_keys(Keys.CONTROL,'x')
time.sleep(2)
#ctrl+x
driver.find_element_by_id("kw").send_keys(Keys.CONTROL,'v')
time.sleep(2)
#ctrl+v
driver.find_element_by_id("su").send_keys(Keys.ENTER)
# Use enter Replace stand-alone operation 
time.sleep(4)
# wait 4 second 
driver.quit()
# Close the browser