爬虫之Selenium库

官方文档:https://selenium-python.readthedocs.io/

Selenium: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。

一、开始

基本使用

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()
try:
    browser.get("https://www.baidu.com")
    input = browser.find_element_by_id("kw")  # 查找id为kw的元素
    input.send_keys("Python")                 # 相当于在输入框输入Python
    input.send_keys(Keys.ENTER)               # 回车
    wait = WebDriverWait(browser, 10)
    # 等待id为content_left的元素加载出来
    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.Edge()
browser = webdriver.PhantomJS()
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()

二、查找元素

单个元素

from selenium import webdriver

browser = webdriver.Chrome()
browser.get("https://www.taobao.com")
# 查找id为q的元素
input1 = browser.find_element_by_id("q")
# CSS选择器选择元素
input2 = browser.find_element_by_css_selector("#q")
# xpath选择元素
input3 = browser.find_element_by_xpath("//*[@id='q']")
print(input1, input2, input3)
"""
<selenium.webdriver.remote.webelement.WebElement (session="7b4386265c07c8e860a4e57cf7f15e6a", element="0.2418348835793498-1")>
<selenium.webdriver.remote.webelement.WebElement (session="7b4386265c07c8e860a4e57cf7f15e6a", element="0.2418348835793498-1")>
<selenium.webdriver.remote.webelement.WebElement (session="7b4386265c07c8e860a4e57cf7f15e6a", element="0.2418348835793498-1")>
"""
browser.close()

查找方式:

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
View Code

通用查找方式:

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

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

多个元素

实际上就是复数的区别。

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

browser = webdriver.Chrome()
browser.get("https://www.taobao.com")

li = browser.find_elements_by_css_selector(".service-bd li")
print(li)
browser.close()
####################
li = browser.find_elements(By.CSS_SELECTOR, ".service-bd li")
print(li)
browser.close()

查找方式: 

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
View Code

三、元素交互操作

对获取的元素调用交互方法。

import time
from selenium import webdriver

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()

更多操作:https://selenium-python.readthedocs.io/api.html#module-selenium.webdriver.remote.webelement

四、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()  # 执行这个动作

效果:

 

更多操作:https://selenium-python.readthedocs.io/api.html#module-selenium.webdriver.common.action_chains

五、执行JavaScript

实现滚动条下拉:

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')")

六、获取元素信息

获取属性

from selenium import webdriver

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"))

获取文本值

from selenium import webdriver

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

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)
input = browser.find_element_by_class_name("zu-top-add-question")
print(input.id)         # 0.11034585982176792-1
print(input.location)   # {'x': 675, 'y': 7}
print(input.tag_name)   # button
print(input.size)       # {'width': 66, 'height': 32}

Frame

在父级frame查找子元素frame,必须要切换到这个frame里面才能实现。

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)  # <selenium.webdriver.remote.webelement.WebElement (session="89ada324d9e5476b0fbb4f62392f31df", element="0.4817565418291889-1")>
try:
    # 如果在frame里面查找frame外面的元素,很可能会报错
    logo1 = browser.find_element_by_class_name("logo")
except NoSuchElementException:    # 找不到元素错误
    print("No logo")              # No logo
browser.switch_to.parent_frame()  # 切换到父frame
logo2 = browser.find_element_by_class_name("logo")
print(logo2)
print(logo2.text)  # RUNOOB.COM

七、等待

如果某些元素没有加载出来/完成,将会导致一些问题。所以应该设置等待,延长时间,确保元素完全都加载出来后,再进行一些操作,这样就可以避免一些异常出现。

隐式等待(如果网速特别慢,则可以使用)

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,默认的时间是0。

from selenium import webdriver

browser = webdriver.Chrome()
browser.implicitly_wait(10)
browser.get("https://www.zhihu.com/explore")
# 如果网速特别慢,导致类属性值为zu-top-add-question这个元素没有加载出来,将会再等待10s
input = browser.find_element_by_class_name("zu-top-add-question")
print(input)

显式等待(常用)

你指定一个等待条件,再指定一个最长等待时间。显示等待会在最长等待时间内判断这个条件是否成立,如果成立则立即返回;如果不成立则会一直等待,直到等待到最长等待时间,如果还是不满足这个条件,就会抛出异常。

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)  # 10代表最长等待时间
# 使用until传入等待条件
input = wait.until(EC.presence_of_element_located((By.ID, "q")))  # 判断id为q的元素是否出现了
button = wait.until(EC.element_to_be_clickable((By.CSS_SELECTOR, ".btn-search")))  # 判断这个元素是否可点击
print(input, button)

判断条件:

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

更多详细内容:https://selenium-python.readthedocs.io/api.html#module-selenium.webdriver.support.expected_conditions

七、前进后退

import time
from selenium import webdriver

browser = webdriver.Chrome()
browser.get("https://www.baidu.com/")
browser.get("https://www.sogou.com/")
browser.get("https://cn.bing.com/")
browser.back()
time.sleep(1)
browser.forward()
time.sleep(1)
browser.close()

八、Cookies

from selenium import webdriver

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

九、标签页(窗口)切换

import time
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.sogou.com/")
time.sleep(1)
browser.switch_to.window(browser.window_handles[0])
browser.get("https://cn.bing.com/")
browser.close()

十、异常处理

from selenium import webdriver

browser = webdriver.Chrome()
browser.get("https://www.baidu.com")
browser.find_element_by_id("hello")
browser.close()
"""
Traceback (most recent call last):
  File "E:/LearnPython/spider/request.py", line 3, in <module>
    browser = webdriver.Chrome()
  File "C:\Python3\lib\site-packages\selenium\webdriver\chrome\webdriver.py", line 81, in __init__
    desired_capabilities=desired_capabilities)
  File "C:\Python3\lib\site-packages\selenium\webdriver\remote\webdriver.py", line 157, in __init__
    self.start_session(capabilities, browser_profile)
  File "C:\Python3\lib\site-packages\selenium\webdriver\remote\webdriver.py", line 252, in start_session
    response = self.execute(Command.NEW_SESSION, parameters)
  File "C:\Python3\lib\site-packages\selenium\webdriver\remote\webdriver.py", line 321, in execute
    self.error_handler.check_response(response)
  File "C:\Python3\lib\site-packages\selenium\webdriver\remote\errorhandler.py", line 242, in check_response
    raise exception_class(message, screen, stacktrace)
selenium.common.exceptions.SessionNotCreatedException: Message: session not created
from disconnected: received Inspector.detached event
  (Session info: chrome=73.0.3683.86)
  (Driver info: chromedriver=2.46.628402 (536cd7adbad73a3783fdc2cab92ab2ba7ec361e1),platform=Windows NT 6.1.7601 SP1 x86_64)
"""
发生异常

捕获异常:

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

browser = webdriver.Chrome()
try:
    browser.get("https://www.baidu.com")
except TimeoutException:
    print("Timeout")
try:
    browser.find_element_by_id("hello")
except NoSuchElementException:
    print("NoSuchElement")
finally:
    browser.close()

详细文档:https://selenium-python.readthedocs.io/api.html#module-selenium.common.exceptions

 

posted @ 2019-04-05 09:17  就俗人一个  阅读(231)  评论(0编辑  收藏  举报