from time import *  
from selenium import webdriver

def login(self,username,passwd):
    self.dr=webdriver.Chrome()
    self.dr.implicitly_wait(10)------隐式等待
    self.dr.get('具体网址eg:http://baidu.com')   -----
    self.dr.find_element_by_xpath("//img[@src='themes/default/images/bnt_log.gif']").click()
    self.dr.find_element_by_name('username').send_keys(username)
    self.dr.find_element_by_name('password').send_keys(passwd)
    self.dr.find_element_by_name('submit').click()
    sleep(5)

def logout(self):
    sleep(3)
    self.dr.quit()----