爬虫之Selenium库

ゝ一世哀愁。 2022-01-06 22:03 359阅读 0赞

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

![ContractedBlock.gif][] ![ExpandedBlockStart.gif][]

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

**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：**

![ContractedBlock.gif][] ![ExpandedBlockStart.gif][]

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

## 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][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：

![1468833-20190405093426909-1430811492.gif][]

更多操作：[https://selenium-python.readthedocs.io/api.html\#module-selenium.webdriver.common.action\_chains][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 ###

### 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][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 ##

![ContractedBlock.gif][] ![ExpandedBlockStart.gif][]

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][https_selenium-python.readthedocs.io_api.html_module-selenium.common.exceptions]

转载于:https://www.cnblogs.com/believepd/p/10657953.html

[https_selenium-python.readthedocs.io]: https://selenium-python.readthedocs.io/
[ContractedBlock.gif]: https://images.cnblogs.com/OutliningIndicators/ContractedBlock.gif
[ExpandedBlockStart.gif]: /images/20211227/95ac55a12cff44e9845769066a6abf63.png
[https_selenium-python.readthedocs.io_api.html_module-selenium.webdriver.remote.webelement]: https://selenium-python.readthedocs.io/api.html#module-selenium.webdriver.remote.webelement
[1468833-20190405093426909-1430811492.gif]: /images/20211227/e51f724ad8624186be7504dfbfd0ff1c.png
[https_selenium-python.readthedocs.io_api.html_module-selenium.webdriver.common.action_chains]: https://selenium-python.readthedocs.io/api.html#module-selenium.webdriver.common.action_chains
[https_selenium-python.readthedocs.io_api.html_module-selenium.webdriver.support.expected_conditions]: https://selenium-python.readthedocs.io/api.html#module-selenium.webdriver.support.expected_conditions
[https_selenium-python.readthedocs.io_api.html_module-selenium.common.exceptions]: https://selenium-python.readthedocs.io/api.html#module-selenium.common.exceptions