scrapy框架

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组件

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Scrapy Engine
引擎负责控制数据流在系统中所有组件中流动，并在相应动作发生时触发事件。 详细内容查看下面的数据流(Data Flow)部分。
调度器(Scheduler)
调度器从引擎接受request并将他们入队，以便之后引擎请求他们时提供给引擎。
下载器(Downloader)
下载器负责获取页面数据并提供给引擎，而后提供给spider。
Spiders
Spider是Scrapy用户编写用于分析response并提取item(即获取到的item)或额外跟进的URL的类。 每个spider负责处理一个特定(或一些)网站。 更多内容请看 Spiders 。
Item Pipeline
Item Pipeline负责处理被spider提取出来的item。典型的处理有清理、 验证及持久化(例如存取到数据库中)。 更多内容查看 Item Pipeline 。
下载器中间件(Downloader middlewares)
下载器中间件是在引擎及下载器之间的特定钩子(specific hook)，处理Downloader传递给引擎的response。 其提供了一个简便的机制，通过插入自定义代码来扩展Scrapy功能。更多内容请看 下载器中间件(Downloader Middleware) 。
Spider中间件(Spider middlewares)
Spider中间件是在引擎及Spider之间的特定钩子(specific hook)，处理spider的输入(response)和输出(items及requests)。 其提供了一个简便的机制，通过插入自定义代码来扩展Scrapy功能。更多内容请看 Spider中间件(Middleware) 。

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数据流

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1. 首先，引擎从调度器中取出一个链接(URL)用于接下来的抓取
2. 引擎把URL封装成一个请求(Request)传给下载器，下载器把资源下载下来，并封装成应答(Response)
3. 然后，爬虫解析Response 若是解析出实体（Item）,则交给实体管道进行进一步的处理。
4. 若是解析出的是链接（URL）,则把URL交给调度器等待抓取

官方文档

# -*- coding: utf-8 -*-

# Scrapy settings for swust project
#
# For simplicity, this file contains only settings considered important or
# commonly used. You can find more settings consulting the documentation:
#
# http://doc.scrapy.org/en/latest/topics/settings.html
# http://scrapy.readthedocs.org/en/latest/topics/downloader-middleware.html
# http://scrapy.readthedocs.org/en/latest/topics/spider-middleware.html

BOT_NAME = 'swust'

SPIDER_MODULES = ['swust.spiders']
NEWSPIDER_MODULE = 'swust.spiders'


# Crawl responsibly by identifying yourself (and your website) on the user-agent
#USER_AGENT = 'swust (+http://www.yourdomain.com)'

# Configure maximum concurrent requests performed by Scrapy (default: 16)
'Item Processor(即 Item Pipeline) 同时处理(每个response的)item的最大值。'
CONCURRENT_REQUESTS=32

# Configure a delay for requests for the same website (default: 0)
# See http://scrapy.readthedocs.org/en/latest/topics/settings.html#download-delay
# See also autothrottle settings and docs
'下载器在下载同一个网站下一个页面前需要等待的时间。该选项可以用来限制爬取速度， 减轻服务器压力。同时也支持小数'
DOWNLOAD_DELAY=3
'该随机值降低了crawler被检测到(接着被block)的机会。某些网站会分析请求， 查找请求之间时间的相似性。'
RANDOMIZE_DOWNLOAD_DELAY=True
# The download delay setting will honor only one of:
'Scrapy downloader 并发请求(concurrent requests)的最大值。'
CONCURRENT_REQUESTS_PER_DOMAIN=32
'对单个IP进行并发请求的最大值。如果非0，则忽略 CONCURRENT_REQUESTS_PER_DOMAIN 设定， 使用该设定。 也就是说，并发限制将针对IP，而不是网站。'
# CONCURRENT_REQUESTS_PER_IP=16

'最大爬取深度'
#DEPTH_LIMIT=0
'深度优先级'
#DEPTH_PRIORITY=0
'是否收集最大深度的数据'
#DEPTH_STATS=True
'是否收集详细的深度数据。如果启用，每个深度的请求数将会被收集在数据中。'
#DEPTH_STATS_VERBOSE=False
'是否启用DNS内存缓存(DNS in-memory cache)。'
#DNSCACHE_ENABLED=True
'最大重定向次数'
#REDIRECT_MAX_TIMES=20
'如果启用，Scrapy将会尊重 robots.txt策略'
#ROBOTSTXT_OBEY=True

'防止被ban'
# Disable cookies (enabled by default)
COOKIES_ENABLED=False

# Disable Telnet Console (enabled by default)
#TELNETCONSOLE_ENABLED=False

# Override the default request headers:
#DEFAULT_REQUEST_HEADERS = {
# 'Accept': 'text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8',
# 'Accept-Language': 'en',
#}

# Enable or disable spider middlewares
# See http://scrapy.readthedocs.org/en/latest/topics/spider-middleware.html
#SPIDER_MIDDLEWARES = {
# 'swust.middlewares.MyCustomSpiderMiddleware': 543,
#}

# Enable or disable downloader middlewares
# See http://scrapy.readthedocs.org/en/latest/topics/downloader-middleware.html
DOWNLOADER_MIDDLEWARES = {
   # 'swust.middlewares.MyCustomDownloaderMiddleware': 543,
   'scrapy.downloadermiddlewares.useragent.UserAgentMiddleware' : None,
   'swust.middlewares.RotateUserAgentMiddleware' : 543
}

# '覆盖默认的 user-agent，最好使用数据库等动态管理'
# USER_AGENTS = [
# "Mozilla/4.0 (compatible; MSIE 6.0; Windows NT 5.1; SV1; AcooBrowser; .NET CLR 1.1.4322; .NET CLR 2.0.50727)",
# "Mozilla/4.0 (compatible; MSIE 7.0; Windows NT 6.0; Acoo Browser; SLCC1; .NET CLR 2.0.50727; Media Center PC 5.0; .NET CLR 3.0.04506)",
# "Mozilla/4.0 (compatible; MSIE 7.0; AOL 9.5; AOLBuild 4337.35; Windows NT 5.1; .NET CLR 1.1.4322; .NET CLR 2.0.50727)",
# "Mozilla/5.0 (Windows; U; MSIE 9.0; Windows NT 9.0; en-US)",
# "Mozilla/5.0 (compatible; MSIE 9.0; Windows NT 6.1; Win64; x64; Trident/5.0; .NET CLR 3.5.30729; .NET CLR 3.0.30729; .NET CLR 2.0.50727; Media Center PC 6.0)",
# "Mozilla/5.0 (compatible; MSIE 8.0; Windows NT 6.0; Trident/4.0; WOW64; Trident/4.0; SLCC2; .NET CLR 2.0.50727; .NET CLR 3.5.30729; .NET CLR 3.0.30729; .NET CLR 1.0.3705; .NET CLR 1.1.4322)",
# "Mozilla/4.0 (compatible; MSIE 7.0b; Windows NT 5.2; .NET CLR 1.1.4322; .NET CLR 2.0.50727; InfoPath.2; .NET CLR 3.0.04506.30)",
# "Mozilla/5.0 (Windows; U; Windows NT 5.1; zh-CN) AppleWebKit/523.15 (KHTML, like Gecko, Safari/419.3) Arora/0.3 (Change: 287 c9dfb30)",
# "Mozilla/5.0 (X11; U; Linux; en-US) AppleWebKit/527+ (KHTML, like Gecko, Safari/419.3) Arora/0.6",
# "Mozilla/5.0 (Windows; U; Windows NT 5.1; en-US; rv:1.8.1.2pre) Gecko/20070215 K-Ninja/2.1.1",
# "Mozilla/5.0 (Windows; U; Windows NT 5.1; zh-CN; rv:1.9) Gecko/20080705 Firefox/3.0 Kapiko/3.0",
# "Mozilla/5.0 (X11; Linux i686; U;) Gecko/20070322 Kazehakase/0.4.5",
# "Mozilla/5.0 (X11; U; Linux i686; en-US; rv:1.9.0.8) Gecko Fedora/1.9.0.8-1.fc10 Kazehakase/0.5.6",
# "Mozilla/5.0 (Windows NT 6.1; WOW64) AppleWebKit/535.11 (KHTML, like Gecko) Chrome/17.0.963.56 Safari/535.11",
# "Mozilla/5.0 (Macintosh; Intel Mac OS X 10_7_3) AppleWebKit/535.20 (KHTML, like Gecko) Chrome/19.0.1036.7 Safari/535.20",
# "Opera/9.80 (Macintosh; Intel Mac OS X 10.6.8; U; fr) Presto/2.9.168 Version/11.52",
# ]

# Enable or disable extensions
# See http://scrapy.readthedocs.org/en/latest/topics/extensions.html
#EXTENSIONS = {
# 'scrapy.telnet.TelnetConsole': None,
#}

# Configure item pipelines
# See http://scrapy.readthedocs.org/en/latest/topics/item-pipeline.html
# ITEM_PIPELINES = {
# 'swust.pipelines.SwustPipeline': 300,
# }

# Enable and configure the AutoThrottle extension (disabled by default)
# See http://doc.scrapy.org/en/latest/topics/autothrottle.html
# NOTE: AutoThrottle will honour the standard settings for concurrency and delay
'自动调节爬取速度'
AUTOTHROTTLE_ENABLED=True
# The initial download delay
AUTOTHROTTLE_START_DELAY=5
# The maximum download delay to be set in case of high latencies
AUTOTHROTTLE_MAX_DELAY=60
# Enable showing throttling stats for every response received:
#AUTOTHROTTLE_DEBUG=False

# Enable and configure HTTP caching (disabled by default)
# See http://scrapy.readthedocs.org/en/latest/topics/downloader-middleware.html#httpcache-middleware-settings
#HTTPCACHE_ENABLED=True
#HTTPCACHE_EXPIRATION_SECS=0
#HTTPCACHE_DIR='httpcache'
#HTTPCACHE_IGNORE_HTTP_CODES=[]
#HTTPCACHE_STORAGE='scrapy.extensions.httpcache.FilesystemCacheStorage'