Python爬虫系列-Selenium详解

自动化测试工具，支持多种浏览器。爬虫中主要用来解决JavaScript渲染的问题。

用法讲解

模拟百度搜索网站过程：

from selenium import webdriver
from selenium.webdriver.common.by import By
from selenium.webdriver.common.keys import Keys
from selenium.webdriver.support import expected_conditions as EC
from selenium.webdriver.support.wait import WebDriverWait

browser = webdriver.Chrome() # 声明浏览器对象
try:
  browser.get('https://www.baidu.com')
  input = browser.find_element_by_id('kw')
  input.send_keys('Python')
  input.send_keys(Keys.ENTER)
  wait = WebDriverWait(browser,10)
  wait.until(EC.presence_of_element_located((By.ID,'content_left')))
  print(browser.current_url)
  print(browser.get_cookies())
  print(browser.page_source())
finally:
  browser.close()

声明浏览器对象

from selenium import webdriver

browser = webdriver.Chrome()
browser = webdriver.Firefox()
browser = webdriver.Safari()

访问页面

from selenium import webdriver

browser = webdriver.Chrome()
browser.get('https://www.taobao.com')
print(browser.page_source)
browser.close()
~

查找元素

单个元素

from selenium import webdriver

browser = webdriver.Chrome()
browser.get('https://www.taobao.com')
input_first = browser.find_element_by_id('q')
input_second = browser.find_element_by_css_selector('#q')
input_third = browser.find_element_by_xpath('//*[@id="q"]')
print(input_first,input_second,input_third)
browser.close()

输出结果：

<selenium.webdriver.remote.webelement.WebElement (session="5871542b8137fd6a37c24e8ceb6ca644", element="0.26013942424402736-1")>

<selenium.webdriver.remote.webelement.WebElement (session="5871542b8137fd6a37c24e8ceb6ca644", element="0.26013942424402736-1")>

<selenium.webdriver.remote.webelement.WebElement (session="5871542b8137fd6a37c24e8ceb6ca644", element="0.26013942424402736-1")>

常用的一些方法：

• find_element_by_name
• find_element_by_xpath
• find_element_by_link_text
• find_element_by_partial_link_text
• find_element_by_tag_name
• find_element_by_class_name
• find_element_by_css_selector

from selenium import webdriver
from selenium.webdriver.common.by import By

browser = webdriver.Chrome()
browser.get('https://www.taobao.com')
input_third = browser.find_element(By.ID,'q')
print(input_third)
browser.close()

<selenium.webdriver.remote.webelement.WebElement (session="022c5603607ebd3b1268c4e4f776be87", element="0.07727375735629027-1")>

多个元素

element变为elements，其他没变化

from selenium import webdriver

browser = webdriver.Chrome()
browser.get('https://www.taobao.com')
lis = browser.find_elements_by_css_selector('.service-bd li')
print(lis)
browser.close()

from selenium import webdriver
from selenium.webdriver.common.by import By

browser = webdriver.Chrome()
browser.get('https://www.taobao.com')
lis = browser.find_elements(By.CSS_SELECTOR,'.service-bd li')
print(lis)
browser.close()

常用的一些方法：

• find_elements_by_name
• find_elements_by_xpath
• find_elements_by_link_text
• find_elements_by_partial_link_text
• find_elements_by_tag_name
• find_elements_by_class_name
• find_elements_by_css_selector

元素交互操作

对获取的元素调用交互方法

from selenium import webdriver
import time

browser = webdriver.Chrome()
browser.get('https://www.taobao.com')
input = browser.find_element_by_id('q')
input.send_keys('iPhone')
time.sleep(1)
input.clear()
input.send_keys('iPad')
button = browser.find_element_by_class_name('btn-search')
button.click()

交互动作

将动作附加到动作链中串行执行

from selenium import webdriver
from selenium.webdriver import ActionChains

browser = webdriver.Chrome()
url = 'http://www.runoob.com/try/try.php?filename=jqueryui-api-droppable'
browser.get(url)
browser.switch_to.frame('iframeResult')
source = browser.find_element_by_css_selector('#draggable')
target = browser.find_element_by_css_selector('#droppable')
actions = ActionChains(browser)
actions.drag_and_drop(source,target)
actions.perform()

执行JavaScript操作

把知乎拉到最下面：

from selenium import webdriver

browser = webdriver.Chrome()
browser.get('https://www.zhihu.com/explore')
browser.execute_script('window.scrollTo(0,document.body.scrollHeight)')
browser.execute_script('alert("To Bottom")')

获取元素信息

获取属性

from selenium import webdriver
from selenium.webdriver import ActionChains

browser = webdriver.Chrome()
url = 'https://www.zhihu.com/explore'
browser.get(url)
logo = browser.find_element_by_id('zh-top-link-logo')
print(logo)
print(logo.get_attribute('class'))

<selenium.webdriver.remote.webelement.WebElement (session="d35b5df5c39c24aae9b503846031b648", element="0.12337107958017368-1")>

zu-top-link-logo

获取文本值

from selenium import webdriver

browser = webdriver.Chrome()
url = 'https://www.zhihu.com/explore'
browser.get(url)
i = browser.find_element_by_class_name('zu-top-add-question')
print(i.text)
browser.close()

提问

获取ID、位置、标签名、大小

from selenium import webdriver

browser = webdriver.Chrome()
url = 'https://www.zhihu.com/explore'
browser.get(url)
i = browser.find_element_by_class_name('zu-top-add-question')
print(i.id)
print(i.location)
print(i.tag_name)
print(i.size)
browser.close()

0.25584226320534253-1

{'x': 651, 'y': 7}

button

{'height': 32, 'width': 66}

Frame

在子Frame里面无法查找父Frame里面的元素：

import time
from selenium import webdriver
from selenium.common.exceptions import NoSuchElementException

browser = webdriver.Chrome()
url = 'http://www.runoob.com/try/try.php?filename=jqueryui-api-droppable'
browser.get(url)
browser.switch_to.frame('iframeResult')
source = browser.find_element_by_css_selector('#draggable')
print(source)
try:
  logo = browser.find_element_by_class_name('logo')
except NoSuchElementException:
  print('No Logo')
browser.switch_to.parent_frame()
logo = browser.find_element_by_class_name('logo')
print(logo)
print(logo.text)

显示如下：

<selenium.webdriver.remote.webelement.WebElement (session="a1e6dba0e8fba300e4c57efaed1734ac", element="0.5033848821354301-1")>

No Logo

<selenium.webdriver.remote.webelement.WebElement (session="a1e6dba0e8fba300e4c57efaed1734ac", element="0.7358889613858988-2")>

RUNOOB.COM

等待

隐式等待

当使用了隐式等待执行测试的时候，如果WebDriver没有在DOM中找到元素，将继续等待，超出设定时间后则抛出找不到元素的异常，换句话说，当查找元素或元素并没有立即出现的时候，隐式等待将等待一段时间再查找DOM，默认时间是0

from selenium import webdriver

browser = webdriver.Chrome()
browser.implicitly_wait(10)
browser.get('https://www.zhihu.com/explore')
input = browser.find_element_by_class_name('zu-top-add-question')
print(input)

显示等待

可以判断一些条件是否满足

from selenium import webdriver
from selenium.webdriver.common.by import By
from selenium.webdriver.support.ui import WebDriverWait
from selenium.webdriver.support import expected_conditions as EC

browser = webdriver.Chrome()
browser.get('https://www.taobao.com')
wait = WebDriverWait(browser,10)
input = wait.until(EC.presence_of_element_located((By.ID,'q')))
button = wait.until(EC.element_to_be_clickable((By.CSS_SELECTOR,'.btn-search')))
print(input,button)

<selenium.webdriver.remote.webelement.WebElement (session="eb554e111bd2e93c6f5c74b1ee29b705", element="0.663002834243013-1")> <selenium.webdriver.remote.webelement.WebElement (session="eb554e111bd2e93c6f5c74b1ee29b705", element="0.663002834243013-2")>

• title_is 标题是某内容
• title_contains 标题包含某内容
• presence_of_element_located 元素加载出，传入定位元组，如(By.ID,'p')
• visibility_of_element_located 元素可见，传入定位元组
• visibility_of 可见，传入元素对象
• presence_of_all_elements_located 所有元素加载出
• text_to_be_present_in_element 某个元素文本包含某文字
• text_to_be_present_in_element_value 某个元素值包含某文字
• frame_to_be_available_and_switch_to_it frame加载并切换
• invisibility_of _element_located 元素不可见
• element_to_be_clickable 元素可点击
• staleness_of 判断一个元素是否仍在DOM，可判断页面是否已经刷新
• element_to_be_selected 元素可选择，传元素对象
• element_located_to_be_selected 元素可选择，传入定位元组
• element_selection_state_to_be 传入元素对象以及状态，相等返回True，否则返回False
• element_located_selection_state_to_be 传入定位元组以及状态，相等返回True，否则返回False
• alert_is_present 是否出现Alert

前进后退

import time
from selenium import webdriver

browser = webdriver.Chrome()
browser.get('https://www.baidu.com/')
browser.get('https://www.taobao.com/')
browser.get('https://www.sina.com/')
browser.back()
time.sleep(1)
browser.forward()
browser.close()

Cookies

from selenium import webdriver

browser = webdriver.Chrome()
browser.get('https://www.zhihu.com/explore')
print(browser.get_cookies())
browser.add_cookie({'name':'name','domain':'www.zhihu.com','value':'germey'})
print(browser.get_cookies())
browser.delete_all_cookies()
print(browser.get_cookies())

选项卡管理

import time

打开两个窗口，并在第一个窗口跳转到第三个网页

from selenium import webdriver

browser = webdriver.Chrome()
browser.get('https://www.baidu.com')
browser.execute_script('window.open()')
print(browser.window_handles)
browser.switch_to_window(browser.window_handles[1])
browser.get('https://www.taobao.com')
time.sleep(1)
browser.switch_to_window(browser.window_handles[0])
browser.get('https://python.org')

异常处理

from selenium import webdriver

browser = webdriver.Chrome()
browser.get('https://www.baidu.com')
browser.find_element_by_id('hello')

Traceback (most recent call last):

File "basic3.py", line 5, in

browser.find_element_by_id('hello')

raise exception_class(message, screen, stacktrace)

selenium.common.exceptions.NoSuchElementException: Message: no such element: Unable to locate element: {"method":"id","selector":"hello"}

(Session info: chrome=70.0.3538.77)

(Driver info: chromedriver=2.43.600233 (523efee95e3d68b8719b3a1c83051aa63aa6b10d),platform=Linux 4.15.0-39-generic x86_64)

from selenium import webdriver
from selenium.common.exceptions import TimeoutException,NoSuchElementException

browser = webdriver.Chrome()
try:
  browser.get('https://www.baidu.com')
except TimeoutException:
  print('Time Out')
try:
  browser.find_element_by_id('hello')
except NoSuchElementException:
  print('No Element')
finally:
  browser.close()