1、XPath是什么？
XPath即XML路径语言(XML Path Language)，它是一种用来确定xml文档中某部分位置的语言。XPath本身遵循w3c标准。
xml文档(html属于xml)是由一系列结点构成的树。例如从网络上爬取的一段html代码：
<div class="post-114638 post type-post status-publish format-standard hentry category-it-tech tag-linux odd" id="post-114638">
<!-- BEGIN .entry-header -->
<div class="entry-header">
<h1>能从远程获得乐趣的 Linux 命令</h1>
</div>
<div class="entry-meta">
<p class="entry-meta-hide-on-mobile">
2019/01/13 · <a href="http://blog.jobbole.com/category/it-tech/" rel="category tag">IT技术</a>
· <a href="http://blog.jobbole.com/tag/linux/">Linux</a>
</p>
</div>
<!-- END .entry-meta -->
<div class="entry"></div>
<div class="textwidget"></div>
</div>2、利用Scrapy提供的shell进行XPath的调试
自己构建Selector对象
构建Selector对象有多种方式，这里我们只介绍一种简单易用的，便于我们进行XPath的调试、学习即可。
- 创建Selector对象：
In [1]: from scrapy.selector import Selector
In [2]: body = "<book><author>Tom John</author></book>"
In [3]: selector = Selector(text=body)
In [4]: selector
Out[4]: <Selector xpath=None data='<html><body><book><author>Tom John</auth'>- 选中&提取数据：
In [5]: selector.xpath('//book/author/text()')
Out[5]: [<Selector xpath='//book/author/text()' data='Tom John'>]
In [40]: selector.xpath('string(//author)')
Out[40]: [<Selector xpath='string(//author)' data='Tom John'>]正则表达式的使用：
>>> response.xpath('//*[@id="post-114638"]/div[3]/div[5]/span[2]/text()').re('\d*')
['', '1', '', '', '', '']
>>> response.xpath('//*[@id="post-114638"]/div[3]/div[5]/span[2]/text()')
[<Selector xpath='//*[@id="post-114638"]/div[3]/div[5]/span[2]/text()' data=' 1 收藏'>]
>>> response.xpath('//*[@id="post-114638"]/div[3]/div[5]/span[2]/text()').re('\d+')
['1']
>>> response.xpath('//*[@id="post-114638"]/div[3]/div[5]/span[2]/text()').re('\d+')[0]
'1'
>>> response.xpath('//*[@id="post-114638"]/div[3]/div[5]/span[2]/text()').re('.*(\d+).*')[0]
'1'
>>>> response.xpath('//*[@id="post-114638"]/div[3]/div[5]/span[2]/text()').re('.*(\d+).*').group(1)
Traceback (most recent call last):
File "<console>", line 1, in <module>
AttributeError: 'list' object has no attribute 'group'
>>>利用Scrapy提供的shell
利用scrapy提供的shell调试scrapy shell http://blog.jobbole.com/114638/：
(Py3_spider) D:\SpiderProject\spider_pjt1>scrapy shell http://blog.jobbole.com/114638/
2019-01-31 10:37:25 [scrapy.utils.log] INFO: Scrapy 1.5.2 started (bot: spider_pjt1)
2019-01-31 10:37:25 [scrapy.utils.log] INFO: Versions: lxml 4.3.0.0, libxml2 2.9.5, cssselect 1.0.3, parsel 1.5.1, w3lib 1.20.0, Twisted 18.9.0, Python 3.7.1 (v3.7.1:260ec2c36a, Oct 20 2018, 14:57:15) [MSC v.1915 64 bit (AMD64)], pyOpenSSL 19.0.0 (OpenSSL 1.1.1a 20 Nov 2018), cryptography 2.5, Platform Windows-10-10.0.17763-SP0
2019-01-31 10:37:25 [scrapy.crawler] INFO: Overridden settings: {'BOT_NAME': 'spider_pjt1', 'DUPEFILTER_CLASS': 'scrapy.dupefilters.BaseDupeFilter', 'LOGSTATS_INTERVAL': 0, 'NEWSPIDER_MODULE': 'spider_pjt1.spiders', 'SPIDER_MODULES': ['spider_pjt1.spiders']}
2019-01-31 10:37:25 [scrapy.extensions.telnet] INFO: Telnet Password: 4f8f06a70c3e7ec1
2019-01-31 10:37:25 [scrapy.middleware] INFO: Enabled extensions:
['scrapy.extensions.corestats.CoreStats',
'scrapy.extensions.telnet.TelnetConsole']
2019-01-31 10:37:26 [scrapy.middleware] INFO: Enabled downloader middlewares:
['scrapy.downloadermiddlewares.httpauth.HttpAuthMiddleware',
'scrapy.downloadermiddlewares.downloadtimeout.DownloadTimeoutMiddleware',
'scrapy.downloadermiddlewares.defaultheaders.DefaultHeadersMiddleware',
'scrapy.downloadermiddlewares.useragent.UserAgentMiddleware',
'scrapy.downloadermiddlewares.retry.RetryMiddleware',
'scrapy.downloadermiddlewares.redirect.MetaRefreshMiddleware',
'scrapy.downloadermiddlewares.httpcompression.HttpCompressionMiddleware',
'scrapy.downloadermiddlewares.redirect.RedirectMiddleware',
'scrapy.downloadermiddlewares.cookies.CookiesMiddleware',
'scrapy.downloadermiddlewares.httpproxy.HttpProxyMiddleware',
'scrapy.downloadermiddlewares.stats.DownloaderStats']
2019-01-31 10:37:26 [scrapy.middleware] INFO: Enabled spider middlewares:
['scrapy.spidermiddlewares.httperror.HttpErrorMiddleware',
'scrapy.spidermiddlewares.offsite.OffsiteMiddleware',
'scrapy.spidermiddlewares.referer.RefererMiddleware',
'scrapy.spidermiddlewares.urllength.UrlLengthMiddleware',
'scrapy.spidermiddlewares.depth.DepthMiddleware']
2019-01-31 10:37:26 [scrapy.middleware] INFO: Enabled item pipelines:
[]
2019-01-31 10:37:26 [scrapy.extensions.telnet] DEBUG: Telnet console listening on 127.0.0.1:6023
2019-01-31 10:37:26 [scrapy.core.engine] INFO: Spider opened
2019-01-31 10:37:27 [scrapy.core.engine] DEBUG: Crawled (200) <GET http://blog.jobbole.com/114638/> (referer: None)
[s] Available Scrapy objects:
[s] scrapy scrapy module (contains scrapy.Request, scrapy.Selector, etc)
[s] crawler <scrapy.crawler.Crawler object at 0x00000228574EFB70>
[s] item {}
[s] request <GET http://blog.jobbole.com/114638/>
[s] response <200 http://blog.jobbole.com/114638/>
[s] settings <scrapy.settings.Settings object at 0x00000228574EFA90>
[s] spider <JobboleSpider 'jobbole' at 0x22857795d68>
[s] Useful shortcuts:
[s] fetch(url[, redirect=True]) Fetch URL and update local objects (by default, redirects are followed)
[s] fetch(req) Fetch a scrapy.Request and update local objects
[s] shelp() Shell help (print this help)
[s] view(response) View response in a browser
>>>接着就可以在这里进行调试，比如：
>>> title = response.xpath('//*[@id="post-114638"]/div[1]/h1')
>>> title
[<Selector xpath='//*[@id="post-114638"]/div[1]/h1' data='<h1>能从远程获得乐趣的 Linux 命令</h1>'>]
>>>
>>> title.extract()
['<h1>能从远程获得乐趣的 Linux 命令</h1>']
>>> title.extract()[0]
'<h1>能从远程获得乐趣的 Linux 命令</h1>'
>>>由于xpath返回一个selector对象，所以可以接着对其操作：
>>> title.xpath('//div[@class="entry-header"]/h1/text()')
[<Selector xpath='//div[@class="entry-header"]/h1/text()' data='能从远程获得乐趣的 Linux 命令'>]
>>> title.xpath('//div[@class="entry-header"]/h1/text()').extract()
['能从远程获得乐趣的 Linux 命令']
>>> title.xpath('//div[@class="entry-header"]/h1/text()').extract()[0]
'能从远程获得乐趣的 Linux 命令'
>>>注意text只会获取到标签内的文本，在遇到下一个标签时后面的文本都将被忽略，如：
html代码：
<div class="post-114638 post type-post status-publish format-standard hentry category-it-tech tag-linux odd" id="post-114638">
<!-- BEGIN .entry-header -->
<div class="entry-header">
<h1>能从远程获得乐趣的 Linux 命令</h1>
</div>
<div class="entry-meta">
<p class="entry-meta-hide-on-mobile">
2019/01/13 · <a href="http://blog.jobbole.com/category/it-tech/" rel="category tag">IT技术</a>
· <a href="http://blog.jobbole.com/tag/linux/">Linux</a>
</p>
</div>
<!-- END .entry-meta -->
<div class="entry"></div>
<div class="textwidget"></div>
</div>text()获取文本：
>>> response.xpath('//*[@id="post-114638"]/div[2]/p').extract()[0]
'<p class="entry-meta-hide-on-mobile">\r\n\r\n 2019/01/13 · <a href="http://blog.jobbole.com/category/it-tech/" rel="category tag">IT技术</a>\r\n \r\n \r\n\r\n \r\n · <a href="http://blog.jobbole.com/tag/linux/">Linux</a>\r\n \r\n</p>'
>>>
>>> response.xpath('//*[@id="post-114638"]/div[2]/p/text()').extract()[0]
'\r\n\r\n 2019/01/13 · '
>>>
>>> response.xpath('//*[@id="post-114638"]/div[2]/p/text()').extract()[0].replace('·','').strip()
'2019/01/13'
>>>扩展
分析一下下面两个文件的代码：
这是scrapy genspider jobbole blog.jobbole.com自动生成的文件(spider_pjt1\spider_pjt1\spiders\jobbole.py)：
# -*- coding: utf-8 -*-
import scrapy
class JobboleSpider(scrapy.Spider):
name = 'jobbole'
allowed_domains = ['blog.jobbole.com']
start_urls = ['http://blog.jobbole.com/']
def parse(self, response):
pass这个类继承scrapy.Spider，查看一下scrapy.Spider的一段代码(Envs\Py3_spider\Lib\site-packages\scrapy\spiders\__init__.py)：
def start_requests(self):
cls = self.__class__
if method_is_overridden(cls, Spider, 'make_requests_from_url'):
warnings.warn(
"Spider.make_requests_from_url method is deprecated; it "
"won't be called in future Scrapy releases. Please "
"override Spider.start_requests method instead (see %s.%s)." % (
cls.__module__, cls.__name__
),
)
for url in self.start_urls:
yield self.make_requests_from_url(url)
else:
for url in self.start_urls:
yield Request(url, dont_filter=True)
def make_requests_from_url(self, url):
""" This method is deprecated. """
return Request(url, dont_filter=True)scrapy下载器(DOWNLOADER)下载完成后会回到接着执行parse()。parse(self, response)中的response和Django中的response相似。
PyCharm中没有scrapy的模板，可以自己定义main.py文件来调用命令行完成调试，这里用到scrapy提供的内置函数，调用这个函数可以执行scrapy脚本。下面是main.py文件(spider_pjt1\main.py)：
3、在PyCharm等IDE中进行调试
我们选择PyCharm为例，其他IDE类似：
引子：
scrapy启动一个spider的命令：scrapy crawl spider_name，spider_name和JobboleSpider中的name值一致，注意确保在scrapy.cfg所在路径执行命令。
(Py3_spider) D:\SpiderProject>cd spider_pjt1
(Py3_spider) D:\SpiderProject\spider_pjt1>scrapy crawl jobbole
...
ModuleNotFoundError: No module named 'win32api'提示缺失win32api模块。
我们安装pypiwin32，这个一般只是Windows环境下会出现这个问题。
或者使用豆瓣镜像源：pip install -i https://pypi.douban.com/simple pypiwin32
(Py3_spider) D:\SpiderProject\spider_pjt1>pip install pypiwin32
Collecting pypiwin32
Downloading https://files.pythonhosted.org/packages/d0/1b/2f292bbd742e369a100c91faa0483172cd91a1a422a6692055ac920946c5/pypiwin32-223-py3-none-any.whl
Collecting pywin32>=223 (from pypiwin32)
Downloading https://files.pythonhosted.org/packages/a3/8a/eada1e7990202cd27e58eca2a278c344fef190759bbdc8f8f0eb6abeca9c/pywin32-224-cp37-cp37m-win_amd64.whl (9.0MB)
100% |████████████████████████████████| 9.1MB 32kB/s
Installing collected packages: pywin32, pypiwin32
Successfully installed pypiwin32-223 pywin32-224接下来就可以正常启动对应的爬虫了：
(Py3_spider) D:\SpiderProject\spider_pjt1>scrapy crawl jobbole
...
2019-01-31 08:13:48 [scrapy.core.engine] INFO: Spider closed (finished)
(Py3_spider) D:\SpiderProject\spider_pjt1>进入正题：
然后我们main.py的代码如下：
# -*- coding: utf-8 -*-
# @Author : One Fine
# @File : main.py
from scrapy.cmdline import execute
import sys
import os
# 设置项目工程的路径，使scrapy命令在项目工程里面运行
# os.path.abspath(__file__)获取当前文件的路径
# os.path.dirname(os.path.abspath(__file__))获取当前文件所在目录的父目录————即项目所在路径
sys.path.append(os.path.dirname(os.path.abspath(__file__)))
# 调用execute()函数来执行命令，此方法传递一个数组作为参数
execute(["scrapy", "crawl", "jobbole"])接下来设置settings.py中的ROBOTSTXT_OBEY参数，将其改为False，让scrapy在爬取过程中不要读取网站的robots.txt文件，不过滤符合robots协议的url。
ROBOTSTXT_OBEY = False接下来在spider_pjt1\spider_pjt1\spiders\jobbole.py的parse方法内部打上断点就可以从main.py调试scrapy项目了。
注意：F12是全部加载完之后的结构，和直接点击view page source可能不一样——里面的代码是http请求时就产生的。
下面使用XPath提取网页数据：
def parse_detail(self, response):
#获取标题
#可以用//*[@id="post-112614"]/div[1]/h1/text()获取标签里面的值
title = response.xpath('//*[@class="entry-header"]/h1/text()').extract()[0]
# print('title',title)
# re1_selector = response.xpath('//div[@class="entry_header"]/h1/text()')
#获取时间
#获取字符串的话用time.extract()[0].strip().repalce("·","").strip()
create_date = response.xpath('//*[@class="entry-meta-hide-on-mobile"]/text()').extract()[0].strip().replace("·","").strip()
#获取点赞数
praise_nums = response.xpath("//span[contains(@class,'vote-post-up')]/h10/text()").extract()[0]
#获取收藏,此处包含'收藏数'和'收藏'两个字
fav_nums = response.xpath("//span[contains(@class,'bookmark-btn')]/text()").extract()[0].strip()
match_re = re.match('.*?(\d+).*',fav_nums)
if match_re:
#获取收藏数
fav_nums = int(match_re.group(1))
else:
fav_nums = 0
#获取评论数
comment_nums = response.xpath('//*[@class="entry-meta-hide-on-mobile"]/a[2]/text()').extract()[0].strip()
match_re = re.match('.*?(\d+).*', comment_nums)
if match_re:
# 获取收藏数
comment_nums = int(match_re.group(1))
else:
comment_nums = 0
#获取文章分类标签
tag_list = response.xpath("//p[@class='entry-meta-hide-on-mobile']/a/text()").extract()
tag_list = [element for element in tag_list if not element.strip().endswith('评论')]
tag = ','.join(tag_list)
content = response.xpath('//*[@class="entry"]').extract()[0]
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