一. 课程安排

课程内容
- Scrapy log信息的认知
- Scrapy shell
- Scrapy settings说明和配置
- Scrapy CrawlSpider说明

二. 课堂笔记

1. Scrapy log信息的认知

2019-01-19 09:50:48 [scrapy.utils.log] INFO: Scrapy 1.5.1 started (bot: tencent)
2019-01-19 09:50:48 [scrapy.utils.log] INFO: Versions: lxml 4.2.5.0, libxml2 2.9.5, cssselect 1.0.3, parsel 1.5.0, w3lib 1.19.0, Twisted 18.9.0, Python 3.6.5 (v3
.6.5:f59c0932b4, Mar 28 2018, 17:00:18) [MSC v.1900 64 bit (AMD64)], pyOpenSSL 18.0.0 (OpenSSL 1.1.0i  14 Aug 2018), cryptography 2.3.1, Platform Windows-10-10.0
.17134-SP0  ### 爬虫scrpay框架依赖的相关模块和平台的信息
2019-01-19 09:50:48 [scrapy.crawler] INFO: Overridden settings: {'BOT_NAME': 'tencent', 'NEWSPIDER_MODULE': 'tencent.spiders', 'ROBOTSTXT_OBEY': True, 'SPIDER_MO
DULES': ['tencent.spiders'], 'USER_AGENT': 'Mozilla/5.0 (Macintosh; Intel Mac OS X 10_12_5) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/59.0.3071.115 Safari/53
7.36'}  ### 自定义的配置信息哪些被应用了 
2019-01-19 09:50:48 [scrapy.middleware] INFO: Enabled extensions: ### 插件信息
['scrapy.extensions.corestats.CoreStats',
 'scrapy.extensions.telnet.TelnetConsole',
 'scrapy.extensions.logstats.LogStats']
2019-01-19 09:50:48 [scrapy.middleware] INFO: Enabled downloader middlewares: ### 启动的下载器中间件
['scrapy.downloadermiddlewares.robotstxt.RobotsTxtMiddleware',
 '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']
2019-01-19 09:50:48 [scrapy.middleware] INFO: Enabled spider middlewares: ### 启动的爬虫中间件
['scrapy.spidermiddlewares.httperror.HttpErrorMiddleware',
 'scrapy.spidermiddlewares.offsite.OffsiteMiddleware',
 'scrapy.spidermiddlewares.referer.RefererMiddleware',
 'scrapy.spidermiddlewares.urllength.UrlLengthMiddleware',
 'scrapy.spidermiddlewares.depth.DepthMiddleware']
2019-01-19 09:50:48 [scrapy.middleware] INFO: Enabled item pipelines: ### 启动的管道
['tencent.pipelines.TencentPipeline']
2019-01-19 09:50:48 [scrapy.core.engine] INFO: Spider opened ### 开始爬去数据
2019-01-19 09:50:48 [scrapy.extensions.logstats] INFO: Crawled 0 pages (at 0 pages/min), scraped 0 items (at 0 items/min)
2019-01-19 09:50:48 [scrapy.extensions.telnet] DEBUG: Telnet console listening on 127.0.0.1:6023
2019-01-19 09:50:51 [scrapy.core.engine] DEBUG: Crawled (200) <GET https://hr.tencent.com/robots.txt> (referer: None)  ### 抓取robots协议内容
2019-01-19 09:50:51 [scrapy.core.engine] DEBUG: Crawled (200) <GET https://hr.tencent.com/position.php?&start=#a0> (referer: None)  ### start_url发起请求
2019-01-19 09:50:51 [scrapy.spidermiddlewares.offsite] DEBUG: Filtered offsite request to 'hr.tencent.com': <GET https://hr.tencent.com/position.php?&start=>  ### 提示错误，爬虫中通过yeid交给引擎的请求会经过爬虫中间件，由于请求的url超出allowed_domain的范围，被offsitmiddleware 拦截了
2019-01-19 09:50:51 [scrapy.core.engine] INFO: Closing spider (finished) ### 爬虫关闭
2019-01-19 09:50:51 [scrapy.statscollectors] INFO: Dumping Scrapy stats: ### 本次爬虫的信息统计
{'downloader/request_bytes': 630,
 'downloader/request_count': 2,
 'downloader/request_method_count/GET': 2,
 'downloader/response_bytes': 4469,
 'downloader/response_count': 2,
 'downloader/response_status_count/200': 2,
 'finish_reason': 'finished',
 'finish_time': datetime.datetime(2019, 1, 19, 1, 50, 51, 558634),
 'log_count/DEBUG': 4,
 'log_count/INFO': 7,
 'offsite/domains': 1,
 'offsite/filtered': 12,
 'request_depth_max': 1,
 'response_received_count': 2,
 'scheduler/dequeued': 1,
 'scheduler/dequeued/memory': 1,
 'scheduler/enqueued': 1,
 'scheduler/enqueued/memory': 1,
 'start_time': datetime.datetime(2019, 1, 19, 1, 50, 48, 628465)}
2019-01-19 09:50:51 [scrapy.core.engine] INFO: Spider closed (finished)

2. Scrapy shell

Scrapy shell是一个交互终端，我们可以在未启动spider的情况下尝试及调试代码，也可以用来测试XPath表达式

使用方法：
scrapy shell https://www.baidu.com/

response.url:当前相应的URL地址
response.request.url:当前相应的请求的URL地址
response.headers:响应头
response.body:响应体，也就是HTML代码，默认是byte类型
response.requests.headers:当前响应的请求头

3. Scrapy settings说明和配置

为什么需要配置文件：

配置文件存放一些公共的变量(比如数据库的地址，账号密码等)

方便自己和别人修改

一般用全大写字母命名变量名 SQL_HOST = ‘192.168.0.1’

settings文件详细信息：https://www.cnblogs.com/cnkai/p/7399573.html

4. Scrapy CrawlSpider说明

之前的代码中，我们有很大一部分时间在寻找下一页的URL地址或者内容的URL地址上面，这个过程能更简单一些吗？

思路：
1.从response中提取所有的li标签对应的URL地址
2.自动的构造自己resquests请求，发送给引擎

目标：通过爬虫了解crawlspider的使用

生成crawlspider的命令：scrapy genspider -t crawl 爬虫名字域名``<br />

4.1 LinkExtractors链接提取器

使用LinkExtractors可以不用程序员自己提取想要的url，然后发送请求。这些工作都可以交给LinkExtractors，他会在所有爬的页面中找到满足规则的url，实现自动的爬取。

class scrapy.linkextractors.LinkExtractor(
    allow = (),
    deny = (),
    allow_domains = (),
    deny_domains = (),
    deny_extensions = None,
    restrict_xpaths = (),
    tags = ('a','area'),
    attrs = ('href'),
    canonicalize = True,
    unique = True,
    process_value = None
)

主要参数讲解：

allow：允许的url。所有满足这个正则表达式的url都会被提取。
deny：禁止的url。所有满足这个正则表达式的url都不会被提取。
allow_domains：允许的域名。只有在这个里面指定的域名的url才会被提取。
deny_domains：禁止的域名。所有在这个里面指定的域名的url都不会被提取。
restrict_xpaths：严格的xpath。和allow共同过滤链接。

4.2 Rule规则类

定义爬虫的规则类。

class scrapy.spiders.Rule(
    link_extractor, 
    callback = None, 
    cb_kwargs = None, 
    follow = None, 
    process_links = None, 
    process_request = None
)