平时写爬虫的时候并不需要设置setting里所有的参数，今天心血来潮，花了点时间查了一下setting模块创建后自动写入的所有参数的含义，记录一下。
- 模块相关说明信息
# -*- coding: utf-8 -*-
# Scrapy settings for new_center 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
- 项目名字和爬虫模块说明，引擎根据这个信息找到爬虫
BOT_NAME = 'new_center' # 项目名字
SPIDER_MODULES = ['new_center.spiders']
NEWSPIDER_MODULE = 'new_center.spiders'
- 浏览器的USER_AGENT，可以自定义伪装。
# Crawl responsibly by identifying yourself (and your website) on the user-agent
#USER_AGENT = 'new_center (+http://www.yourdomain.com)'
- 是否遵守robots协议，默认是遵守的，可以改成False或将其注释
# Obey robots.txt rules
ROBOTSTXT_OBEY = True
- 设置scrapy爬虫最大的并发请求数量，默认是16
# Configure maximum concurrent requests performed by Scrapy (default: 16)
#CONCURRENT_REQUESTS = 32
- 设置对访问同一个网站进行请求的延时时间，默认情况下，Scrapy在两个请求间不等待一个固定的值，而是使用0.5到1.5之间的一个随机值。
# 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
#DOWNLOAD_DELAY = 3
# The download delay setting will honor only one of:
- 设置对每个网站和每个IP的最大并发请求数量，两个最好只设置一个，如果都设置，则按照限制IP生效。
#CONCURRENT_REQUESTS_PER_DOMAIN = 16
#CONCURRENT_REQUESTS_PER_IP = 16
- 设置是否禁用cookie，目前默认是可用的，去掉注释则禁用
# Disable cookies (enabled by default)
#COOKIES_ENABLED = False
- 设置是否可远程登录控制台，目前默认是可以的，去掉注释则禁用
# Disable Telnet Console (enabled by default)
#TELNETCONSOLE_ENABLED = False
- 用来设置请求头，一般不用，因为请求头可以动态设置
# 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',
#}
- 是否开启使用爬虫spider的中间件,默认不启用，解除注释后启用，后面的数字代表优先级，数字越小，优先级越高
# Enable or disable spider middlewares
# See http://scrapy.readthedocs.org/en/latest/topics/spider-middleware.html
#SPIDER_MIDDLEWARES = {
# 'new_center.middlewares.NewCenterSpiderMiddleware': 543,
#}
- 是否开启爬虫下载器的中间件,默认不启用，解除注释后启用
# Enable or disable downloader middlewares
# See http://scrapy.readthedocs.org/en/latest/topics/downloader-middleware.html
#DOWNLOADER_MIDDLEWARES = {
# 'new_center.middlewares.MyCustomDownloaderMiddleware': 543,
#}
- 是否禁用爬虫扩展，默认禁用，解除注释后将None改成数字，如500，扩展的优先级一般不重要，因为他们并不相互依赖，多个扩展的value值可以写相同。
# Enable or disable extensions
# See http://scrapy.readthedocs.org/en/latest/topics/extensions.html
#EXTENSIONS = {
# 'scrapy.extensions.telnet.TelnetConsole': None,
#}
- 是否开启管道，默认关闭，开启則解除注释。是一个字典，默认为空，值任意，不过一般设置在0-1000之间，值越小优先级越高。
# Configure item pipelines
# See http://scrapy.readthedocs.org/en/latest/topics/item-pipeline.html
#ITEM_PIPELINES = {
# 'new_center.pipelines.NewCenterPipeline': 300,
#}
- 设置自动限速，根据Scrapy服务器及爬取的网站的负载自动限制爬取速度，默认关闭，开启需解除注释。
# Enable and configure the AutoThrottle extension (disabled by default)
# See http://doc.scrapy.org/en/latest/topics/autothrottle.html
#AUTOTHROTTLE_ENABLED = True # 自动限速的开关
# The initial download delay
#AUTOTHROTTLE_START_DELAY = 5 # 初始下载延时
# The maximum download delay to be set in case of high latencies
#AUTOTHROTTLE_MAX_DELAY = 60 # 最大下载延时
# The average number of requests Scrapy should be sending in parallel to
# each remote server
#AUTOTHROTTLE_TARGET_CONCURRENCY = 1.0
# Enable showing throttling stats for every response received:
#AUTOTHROTTLE_DEBUG = False
- 启用和配置HTTP缓存
# 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'
- 另外的重要的设置：
- DEPTH_LIMIT：爬取网站最大的允许深度，默认值为0，表示没有限制；如果为1，表示只允许解析一层的url。
- DOWNLOAD_TIMEOUT:下载器超时时间，默认180s.
- LOG_ENABLED:是否启用logging，即日志文件，默认为True。
- LOG_ENCODING：设置日志文件的编码，默认使用UTF_8。
- LOG_LEVEL：对日志的内容进行等级的设置，有五个级别可以选择:
CRITICAL: 严重错误；
ERROR：一般错误；
WARNING：警告信息；
INFO：一般信息；
DEBUG：调试信息
- PROXIES：设置代理；这不是scrapy内置的参数，但可以定义在setting模块，使用的时候可以导入。