Python开发之爬虫模块介绍（三）

Selenium模块

它是一个自动化测试工具，可以支持多个浏览器，在爬虫中主要用来解决JavaScript渲染的问题。

安装：pip3 install selenium

Selenium用法介绍

1、基本用法

from selenium import webdriver  # webdriver就是一个浏览器驱动对象
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('http://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'))) # 等待content_left被加载出来
    print(browser.current_url)
    print(browser.get_cookies())
    print(browser.page_source)
finally:
    browser.close()

2、声明浏览器对象

from selenium import webdriver

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

3、访问页面

from selenium import webdriver

browser = webdriver.Chrome()
browser.get('http://www.baidu.com')
print(browser.page_source)
browser.close()

4、查找元素

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_elements_by_css_selector('#q')
print(input_first)
print(input_second)
browser.close()

```
browser.find_element_by_id()
```
```
browser.find_element_by_class_name()
```
```
browser.find_element_by_name()
```
```
browser.find_element_by_link_text()
```
```
browser.find_element_by_xpath()
```

browser.find_element_by_partial_link_text()

```
browser.find_element_by_tag_name()
```

　第二种查找元素的方法，通用的方式

from selenium import webdriver
from selenium.webdriver.common.by import By
browser = webdriver.Chrome()
browser.get('https://www.taobao.com')
input_first = browser.find_element(By.ID,'q')
print(input_first)
browser.close()

5、多个元素

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')
lis = browser.find_elements(By.CSS_SELECTOR,'.service-bd li')
print(lis)
browser.close()

6、元素的交互操作

对获得元素调用交互方法

import time
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')
input.send_keys('iphone')
time.sleep(2)
input.clear()
input.send_keys('ipad')
button = browser.find_element_by_class_name('btn-search')
button.click()

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

7、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_elements_by_css_selector('#draggable')
target = browser.find_elements_by_css_selector('#droppable')
actions = ActionChains(browser)
actions.drag_and_drop(source,target)
actions.perform()

8、执行JavaScript

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')")

9、获取元素信息

获取属性

from selenium import webdriver

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

获取位置，ID，标签名，大小

from selenium import webdriver

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

10、Frame

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_elements_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() # 切换父元素的frame
logo = browser.find_element_by_class_name('logo')
print(logo)
print(logo.text)

11、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，超过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')
input = browser.find_element_by_class_name('zu-top-add-question')
print(input.text)

显式等待

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)
print(button)
# EC.title_is # 标题是某内容
# EC.title_contains # 标题包含某内容
# EC.presence_of_element_located # 元素加载出，传入定位元素
# EC.visibility_of # 可见，传入元素对象
# EC.presence_of_all_elements_located # 所有元素加载出
# EC.element_to_be_clickable # 元素可点击
# EC.element_located_to_be_selected # 元素可选择，传定位元素

12、浏览器的前进和后退

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.python.org')
browser.back()
time.sleep(1)
browser.forward()
browser.close()

13、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':'germay'})
print(browser.get_cookies())
browser.delete_all_cookies()
print(browser.get_cookies())

14、选项卡管理

from selenium import webdriver
import time
browser = webdriver.Chrome()
browser.get('https://www.zhihu.com/explore')
browser.execute_script('window.open()')# 新开一个选项卡
print(browser.window_handles) # 所有的选项卡
browser.switch_to.window(browser.window_handles[1]) # 切换
browser.get('https://www.taobao.com')
time.sleep(1)
browser.switch_to.window(browser.window_handles[0]) # 切换回
browser.get('https://www.baidu.com')

15、异常处理

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

browser = webdriver.Chrome()
try:
    browser.get('https://www.taobao.com')
except TimeoutException:
    print('Time out')
try:
    browser.find_element_by_id('hello')
except NoSuchElementException:
    print('NO element')
finally:
    browser.close()

上面只是简单的异常展示，更多异常请参考http://selenium-python.readthedocs.io/api.html#module-selenium.common.exceptions