Python+Selenium定位不到元素常见原因及解决办法(报：NoSuchElementException)

driver=webdriver.Firefox()
driver.get(r'http://www.126.com/')
driver.switch_to_frame('x-URS-iframe') #需先跳转到iframe框架
username=driver.find_element_by_name('email')
username.clear()

#先定位到iframe
elementi= driver.find_element_by_class_name('APP-editor-iframe')
#再将定位对象传给switch_to_frame()方法
driver.switch_to_frame(elementi) 

find_element_by_xpath("//input[@id='kw']")

import time
time.sleep(3)

# coding=utf-8
'''
Created on 2016-7-20
@author: Jennifer
Project:登录百度账号
'''
from selenium import webdriver
import time

driver = webdriver.Firefox()
driver.get("http://www.baidu.com/")

time.sleep(3)

#点击登录：有些name为tj_login的元素为不可见的，点击可见的那个登录按钮即可。
#否则会报：ElementNotVisibleException
element0=driver.find_elements_by_name("tj_login")
for ele0 in element0:
  if ele0.is_displayed():
    ele0.click()

#在登录弹出框，需先定位到登录弹出框
#否则会报：NoSuchElementException
element1=driver.find_element_by_class_name("tang-content")
element11=element1.find_element_by_id("TANGRAM__PSP_8__userName")
element11.clear()
element11.send_keys("登录名")

element2=element1.find_element_by_id("TANGRAM__PSP_8__password")
element2.clear()
element2.send_keys("密码")

element3=element1.find_element_by_id("TANGRAM__PSP_8__submit")
element3.click()
element3.submit()

try:
  assert "登录名" in driver.page_source
except AssertionError:
  print "登录失败"
else:
  print "登录成功"
  time.sleep(3)
finally:
  print "测试记录：已测试"
driver.close()

from selenium import webdriver
from PIL import Image
import time
import pandas as pd
import datetime
 
driver = webdriver.Ie(r"C:\Program Files\internet explorer\IEDriverServer2.exe")
driver.get("https://www.cib.com.cn/cn/minipage/page/login-firmalert.html")
print("请输入用户名和帐号密码，实现登录")
input("====按任意键继续====")
 
# print(driver.current_url) # https://corporatebank.cib.com.cn/firm/main/mainx.do
 
frame = driver.find_element_by_id("workframe") # 切换到 iframe 标签中查找
driver.switch_to_frame(frame) # 切入 iframe 标签
 
# driver.switch_to_default_content()  # 切出 iframe 标签 也可以 直接 默认的
 
driver.find_element_by_xpath('//div[@id="fast-way"]/ul/li[2]/a').click() # 点击 当日明细查询按钮
time.sleep(2)
try:
  driver.find_element_by_xpath('//div[@id="fast-way"]/ul/li[2]/a').click() # 点击 当日明细查询按钮
except Exception as e:
  print("=======双击这个按钮========", e)
time.sleep(3)