第一章 爬虫入门

• Requests和Beautiful Soup 爬取python.org
• urllib3和Beautiful Soup 爬取python.org
• Scrapy 爬取python.org
• Selenium和PhantomJs爬取Python.org

请确认可以打开：https://www.python.org/events/pythonevents
安装好requests、bs4，然后我们开始实例1：Requests和Beautiful Soup 爬取python.org,

# pip3 install requests bs4

Requests和Beautiful Soup 爬取python.org

• 目标： 爬取https://www.python.org/events/python-events/中事件的名称、地点和时间。

01_events_with_requests.py

import requests
from bs4 import BeautifulSoup

def get_upcoming_events(url):
    req = requests.get(url)

    soup = BeautifulSoup(req.text, 'lxml')

    events = soup.find('ul', {'class': 'list-recent-events'}).findAll('li')

    for event in events:
        event_details = dict()
        event_details['name'] = event.find('h3').find("a").text
        event_details['location'] = event.find('span', {'class', 'event-location'}).text
        event_details['time'] = event.find('time').text
        print(event_details)

get_upcoming_events('https://www.python.org/events/python-events/')

执行结果：

$ python3 01_events_with_requests.py 
{'name': 'PyCon US 2018', 'location': 'Cleveland, Ohio, USA', 'time': '09 May – 18 May  2018'}
{'name': 'DjangoCon Europe 2018', 'location': 'Heidelberg, Germany', 'time': '23 May – 28 May  2018'}
{'name': 'PyCon APAC 2018', 'location': 'NUS School of Computing / COM1, 13 Computing Drive, Singapore 117417, Singapore', 'time': '31 May – 03 June  2018'}
{'name': 'PyCon CZ 2018', 'location': 'Prague, Czech Republic', 'time': '01 June – 04 June  2018'}
{'name': 'PyConTW 2018', 'location': 'Taipei, Taiwan', 'time': '01 June – 03 June  2018'}
{'name': 'PyLondinium', 'location': 'London, UK', 'time': '08 June – 11 June  2018'}

注意：因为事件的内容未必相同，所以每次的结果也不会一样

课后习题： 用requests爬取https://china-testing.github.io/首页的博客标题，共10条。

参考答案：

01_blog_title.py

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import requests
from bs4 import BeautifulSoup

def get_upcoming_events(url):
    req = requests.get(url)

    soup = BeautifulSoup(req.text, 'lxml')

    events = soup.findAll('article')

    for event in events:
        event_details = {}
        event_details['name'] = event.find('h1').find("a").text
        print(event_details)

get_upcoming_events('https://china-testing.github.io/')

执行结果：

$ python3 01_blog_title.py 
{'name': '10分钟学会API测试'}
{'name': 'python数据分析快速入门教程4-数据汇聚'}
{'name': 'python数据分析快速入门教程6-重整'}
{'name': 'python数据分析快速入门教程5-处理缺失数据'}
{'name': 'python库介绍-pytesseract: OCR光学字符识别'}
{'name': '软件自动化测试初学者忠告'}
{'name': '使用opencv转换3d图片'}
{'name': 'python opencv3实例(对象识别和增强现实)2-边缘检测和应用图像过滤器'}
{'name': 'numpy学习指南3rd3:常用函数'}
{'name': 'numpy学习指南3rd2:NumPy基础'}

urllib3和Beautiful Soup 爬取python.org

代码：02_events_with_urlib3.py

import urllib3
from bs4 import BeautifulSoup

def get_upcoming_events(url):
    req = urllib3.PoolManager()
    res = req.request('GET', url)

    soup = BeautifulSoup(res.data, 'html.parser')

    events = soup.find('ul', {'class': 'list-recent-events'}).findAll('li')

    for event in events:
        event_details = dict()
        event_details['name'] = event.find('h3').find("a").text
        event_details['location'] = event.find('span', {'class', 'event-location'}).text
        event_details['time'] = event.find('time').text
        print(event_details)

get_upcoming_events('https://www.python.org/events/python-events/')

requests对urllib3进行了封装，一般是直接使用requests。

Scrapy 爬取python.org

Scrapy是用于提取数据的非常流行的开源Python抓取框架。 Scrapy提供所有这些功能以及许多其他内置模块和扩展。当涉及到使用Python进行挖掘时，它也是我们的首选工具。
Scrapy提供了许多值得一提的强大功能：

• 内置的扩展来生成HTTP请求并处理压缩，身份验证，缓存，操作用户代理和HTTP标头
• 内置的支持选择和提取选择器语言如数据CSS和XPath，以及支持使用正则表达式选择内容和链接。
• 编码支持来处理语言和非标准编码声明
• 灵活的API来重用和编写自定义中间件和管道，提供干净而简单的方法来实现自动化等任务。比如下载资产（例如图像或媒体）并将数据存储在存储器中，如文件系统，S3，数据库等

有几种使用Scrapy的方法。一个是程序模式我们在代码中创建抓取工具和蜘蛛。也可以配置Scrapy模板或生成器项目，然后从命令行使用运行。本书将遵循程序模式，因为它的代码在单个文件中。

代码：03_events_with_scrapy.py

import scrapy
from scrapy.crawler import CrawlerProcess

class PythonEventsSpider(scrapy.Spider):
    name = 'pythoneventsspider'

    start_urls = ['https://www.python.org/events/python-events/',]
    found_events = []

    def parse(self, response):
        for event in response.xpath('//ul[contains(@class, "list-recent-events")]/li'):
            event_details = dict()
            event_details['name'] = event.xpath('h3[@class="event-title"]/a/text()').extract_first()
            event_details['location'] = event.xpath('p/span[@class="event-location"]/text()').extract_first()
            event_details['time'] = event.xpath('p/time/text()').extract_first()
            self.found_events.append(event_details)

if __name__ == "__main__":
    process = CrawlerProcess({ 'LOG_LEVEL': 'ERROT630:~/code/china-testing/python3_libraries/pytest_testing/ch2/tasks_proj/tests/func$ pytest test_api_exceptions.py  -v -m "smoke and not get"
=========================================== test session starts ===========================================
platform linux -- Python 3.5.2, pytest-3.5.1, py-1.5.3, pluggy-0.6.0 -- /usr/bin/python3
cachedir: ../.pytest_cache
rootdir: /home/andrew/code/china-testing/python3_libraries/pytest_testing/ch2/tasks_proj/tests, inifile: pytest.ini
collected 7 items / 6 deselected                                                                          

test_api_exceptions.py::test_list_raises PASSED                                                     [100%]
R'})
    process.crawl(PythonEventsSpider)
    spider = next(iter(process.crawlers)).spider
    process.start()

    for event in spider.found_events: print(event)

课后习题： 用scrapy爬取https://china-testing.github.io/首页的博客标题，共10条。

参考答案：

03_blog_with_scrapy.py

from scrapy.crawler import CrawlerProcess

class PythonEventsSpider(scrapy.Spider):
    name = 'pythoneventsspider'

    start_urls = ['https://china-testing.github.io/',]
    found_events = []

    def parse(self, response):
        for event in response.xpath('//article//h1'):
            event_details = dict()
            event_details['name'] = event.xpath('a/text()').extract_first()
            self.found_events.append(event_details)

if __name__ == "__main__":
    process = CrawlerProcess({ 'LOG_LEVEL': 'ERROR'})
    process.crawl(PythonEventsSpider)
    spider = next(iter(process.crawlers)).spider
    process.start()

    for event in spider.found_events: print(event)

Selenium和PhantomJs爬取Python.org

04_events_with_selenium.py

from selenium import webdriver

def get_upcoming_events(url):
    driver = webdriver.Chrome()
    driver.get(url)

    events = driver.find_elements_by_xpath('//ul[contains(@class, "list-recent-events")]/li')

    for event in events:
        event_details = dict()
        event_details['name'] = event.find_element_by_xpath('h3[@class="event-title"]/a').text
        event_details['location'] = event.find_element_by_xpath('p/span[@class="event-location"]').text
        event_details['time'] = event.find_element_by_xpath('p/time').text
        print(event_details)

    driver.close()

get_upcoming_events('https://www.python.org/events/python-events/')

改用driver = webdriver.PhantomJS(‘phantomjs’)可以使用无界面的方式，代码如下：

05_events_with_phantomjs.py

from selenium import webdriver

def get_upcoming_events(url):
    driver = webdriver.Chrome()
    driver.get(url)

    events = driver.find_elements_by_xpath('//ul[contains(@class, "list-recent-events")]/li')

    for event in events:
        event_details = dict()
        event_details['name'] = event.find_element_by_xpath('h3[@class="event-title"]/a').text
        event_details['location'] = event.find_element_by_xpath('p/span[@class="event-location"]').text
        event_details['time'] = event.find_element_by_xpath('p/time').text
        print(event_details)

    driver.close()

get_upcoming_events('https://www.python.org/events/python-events/')

不过selenium的headless模式已经可以更好的代替phantomjs了。

04_events_with_selenium_headless.py

from selenium import webdriver

def get_upcoming_events(url):
    
    options = webdriver.ChromeOptions()
    options.add_argument('headless')
    driver = webdriver.Chrome(chrome_options=options)
    driver.get(url)

    events = driver.find_elements_by_xpath('//ul[contains(@class, "list-recent-events")]/li')

    for event in events:
        event_details = dict()
        event_details['name'] = event.find_element_by_xpath('h3[@class="event-title"]/a').text
        event_details['location'] = event.find_element_by_xpath('p/span[@class="event-location"]').text
        event_details['time'] = event.find_element_by_xpath('p/time').text
        print(event_details)

    driver.close()

get_upcoming_events('https://www.python.org/events/python-events/')

参考资料

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