Python爬虫系列之----Scrapy(六)settings.py配置文件详解

让我们先来看下它里面的内容:

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

# Scrapy settings for demo1 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 = 'demo1'   #Scrapy项目的名字,这将用来构造默认 User-Agent,同时也用来log,当您使用 startproject 命令创建项目时其也被自动赋值。

SPIDER_MODULES = ['demo1.spiders']   #Scrapy搜索spider的模块列表 默认: [xxx.spiders]
NEWSPIDER_MODULE = 'demo1.spiders'   #使用 genspider 命令创建新spider的模块。默认: 'xxx.spiders'


#爬取的默认User-Agent，除非被覆盖
#USER_AGENT = 'demo1 (+http://www.yourdomain.com)'

#如果启用,Scrapy将会采用 robots.txt策略
ROBOTSTXT_OBEY = True

#Scrapy downloader 并发请求(concurrent requests)的最大值,默认: 16
#CONCURRENT_REQUESTS = 32

#为同一网站的请求配置延迟（默认值：0）
# See http://scrapy.readthedocs.org/en/latest/topics/settings.html#download-delay
# See also autothrottle settings and docs  
#DOWNLOAD_DELAY = 3   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:0.25 以秒为单位

    
#下载延迟设置只有一个有效
#CONCURRENT_REQUESTS_PER_DOMAIN = 16   对单个网站进行并发请求的最大值。
#CONCURRENT_REQUESTS_PER_IP = 16       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。该设定也影响 DOWNLOAD_DELAY: 如果 CONCURRENT_REQUESTS_PER_IP 非0,下载延迟应用在IP而不是网站上。

#禁用Cookie（默认情况下启用）
#COOKIES_ENABLED = False

#禁用Telnet控制台（默认启用）
#TELNETCONSOLE_ENABLED = False 

#覆盖默认请求标头：
#DEFAULT_REQUEST_HEADERS = {
#   'Accept': 'text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8',
#   'Accept-Language': 'en',
#}

#启用或禁用蜘蛛中间件
# See http://scrapy.readthedocs.org/en/latest/topics/spider-middleware.html
#SPIDER_MIDDLEWARES = {
#    'demo1.middlewares.Demo1SpiderMiddleware': 543,
#}

#启用或禁用下载器中间件
# See http://scrapy.readthedocs.org/en/latest/topics/downloader-middleware.html
#DOWNLOADER_MIDDLEWARES = {
#    'demo1.middlewares.MyCustomDownloaderMiddleware': 543,
#}

#启用或禁用扩展程序
# See http://scrapy.readthedocs.org/en/latest/topics/extensions.html
#EXTENSIONS = {
#    'scrapy.extensions.telnet.TelnetConsole': None,
#}

#配置项目管道
# See http://scrapy.readthedocs.org/en/latest/topics/item-pipeline.html
#ITEM_PIPELINES = {
#    'demo1.pipelines.Demo1Pipeline': 300,
#}

#启用和配置AutoThrottle扩展（默认情况下禁用）
# See http://doc.scrapy.org/en/latest/topics/autothrottle.html
#AUTOTHROTTLE_ENABLED = True

#初始下载延迟
#AUTOTHROTTLE_START_DELAY = 5

#在高延迟的情况下设置的最大下载延迟
#AUTOTHROTTLE_MAX_DELAY = 60


#Scrapy请求的平均数量应该并行发送每个远程服务器
#AUTOTHROTTLE_TARGET_CONCURRENCY = 1.0

#启用显示所收到的每个响应的调节统计信息：
#AUTOTHROTTLE_DEBUG = False

#启用和配置HTTP缓存（默认情况下禁用）
# 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'

解释几个参数：

ROBOTSTXT_OBEY = True-----------是否遵守robots.txt

CONCURRENT_REQUESTS = 16-----------开启线程数量，默认16

AUTOTHROTTLE_START_DELAY = 3-----------开始下载时限速并延迟时间

AUTOTHROTTLE_MAX_DELAY = 60-----------高并发请求时最大延迟时间

最底下的几个：是否启用在本地缓存，如果开启会优先读取本地缓存，从而加快爬取速度，视情况而定

HTTPCACHE_ENABLED = True

HTTPCACHE_EXPIRATION_SECS = 0

HTTPCACHE_DIR = 'httpcache'

HTTPCACHE_IGNORE_HTTP_CODES = []

HTTPCACHE_STORAGE = 'scrapy.extensions.httpcache.FilesystemCacheStorage'

以上几个可以视项目需要开启，但是有两个参数最好每次都开启，而每次都是项目文件手动开启不免有些麻烦，最好是项目创建后就自动开启


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

这个是浏览器请求头，很多网站都会检查客户端的headers，比如豆瓣就是每一个请求都检查headers的user_agent，否则只会返回403，可以开启

#USER_AGENT = 'Chirco (+http://www.yourdomain.com)'

这个是至关重要的，大部分服务器在请求快了会首先检查User_Agent,而scrapy默认的浏览器头是scrapy1.1 我们需要开启并且修改成浏览器头，如：Mozilla/5.0 (Windows NT 6.1; WOW64) AppleWebKit/537.1 (KHTML, like Gecko) Chrome/22.0.1207.1 Safari/537.1

但是最好是这个USER-AGENT会随机自动更换最好了。

下面的代码可以从预先定义的user-agent的列表中随机选择一个来采集不同的页面 

在settings.py中添加以下代码

DOWNLOADER_MIDDLEWARES = {
    'scrapy.contrib.downloadermiddleware.useragent.UserAgentMiddleware' : None,
    'randoms.rotate_useragent.RotateUserAgentMiddleware' :400
}

rotate_useragent的代码为:

# -*- coding: utf-8 -*-
import random
from scrapy.contrib.downloadermiddleware.useragent import UserAgentMiddleware

class RotateUserAgentMiddleware(UserAgentMiddleware):
    def __init__(self, user_agent=''):
        self.user_agent = user_agent

    def process_request(self, request, spider):
        #这句话用于随机选择user-agent
        ua = random.choice(self.user_agent_list)
        if ua:
            print('User-Agent:'+ua)
            request.headers.setdefault('User-Agent', ua)

    #the default user_agent_list composes chrome,I E,firefox,Mozilla,opera,netscape
    user_agent_list = [\
        "Mozilla/5.0 (Windows NT 6.1; WOW64) AppleWebKit/537.1 (KHTML, like Gecko) Chrome/22.0.1207.1 Safari/537.1"\
        "Mozilla/5.0 (X11; CrOS i686 2268.111.0) AppleWebKit/536.11 (KHTML, like Gecko) Chrome/20.0.1132.57 Safari/536.11",\
        "Mozilla/5.0 (Windows NT 6.1; WOW64) AppleWebKit/536.6 (KHTML, like Gecko) Chrome/20.0.1092.0 Safari/536.6",\
        "Mozilla/5.0 (Windows NT 6.2) AppleWebKit/536.6 (KHTML, like Gecko) Chrome/20.0.1090.0 Safari/536.6",\
        "Mozilla/5.0 (Windows NT 6.2; WOW64) AppleWebKit/537.1 (KHTML, like Gecko) Chrome/19.77.34.5 Safari/537.1",\
        "Mozilla/5.0 (X11; Linux x86_64) AppleWebKit/536.5 (KHTML, like Gecko) Chrome/19.0.1084.9 Safari/536.5",\
        "Mozilla/5.0 (Windows NT 6.0) AppleWebKit/536.5 (KHTML, like Gecko) Chrome/19.0.1084.36 Safari/536.5",\
        "Mozilla/5.0 (Windows NT 6.1; WOW64) AppleWebKit/536.3 (KHTML, like Gecko) Chrome/19.0.1063.0 Safari/536.3",\
        "Mozilla/5.0 (Windows NT 5.1) AppleWebKit/536.3 (KHTML, like Gecko) Chrome/19.0.1063.0 Safari/536.3",\
        "Mozilla/5.0 (Macintosh; Intel Mac OS X 10_8_0) AppleWebKit/536.3 (KHTML, like Gecko) Chrome/19.0.1063.0 Safari/536.3",\
        "Mozilla/5.0 (Windows NT 6.2) AppleWebKit/536.3 (KHTML, like Gecko) Chrome/19.0.1062.0 Safari/536.3",\
        "Mozilla/5.0 (Windows NT 6.1; WOW64) AppleWebKit/536.3 (KHTML, like Gecko) Chrome/19.0.1062.0 Safari/536.3",\
        "Mozilla/5.0 (Windows NT 6.2) AppleWebKit/536.3 (KHTML, like Gecko) Chrome/19.0.1061.1 Safari/536.3",\
        "Mozilla/5.0 (Windows NT 6.1; WOW64) AppleWebKit/536.3 (KHTML, like Gecko) Chrome/19.0.1061.1 Safari/536.3",\
        "Mozilla/5.0 (Windows NT 6.1) AppleWebKit/536.3 (KHTML, like Gecko) Chrome/19.0.1061.1 Safari/536.3",\
        "Mozilla/5.0 (Windows NT 6.2) AppleWebKit/536.3 (KHTML, like Gecko) Chrome/19.0.1061.0 Safari/536.3",\
        "Mozilla/5.0 (X11; Linux x86_64) AppleWebKit/535.24 (KHTML, like Gecko) Chrome/19.0.1055.1 Safari/535.24",\
        "Mozilla/5.0 (Windows NT 6.2; WOW64) AppleWebKit/535.24 (KHTML, like Gecko) Chrome/19.0.1055.1 Safari/535.24"
       ]

运行爬虫可以看到信息:

2017-04-16 00:07:40 [scrapy.extensions.telnet] DEBUG: Telnet console listening on 127.0.0.1:6023
User-Agent:Mozilla/5.0 (Windows NT 6.2) AppleWebKit/536.3 (KHTML, like Gecko) Chrome/19.0.1061.1 Safari/536.3
2017-04-16 00:07:40 [scrapy.downloadermiddlewares.redirect] DEBUG: Redirecting (301) to  from 
User-Agent:Mozilla/5.0 (Windows NT 6.2; WOW64) AppleWebKit/537.1 (KHTML, like Gecko) Chrome/19.77.34.5 Safari/537.1
2017-04-16 00:07:41 [scrapy.core.engine] DEBUG: Crawled (200)  (referer: None)
User-Agent:Mozilla/5.0 (Windows NT 6.2; WOW64) AppleWebKit/535.24 (KHTML, like Gecko) Chrome/19.0.1055.1 Safari/535.24
2017-04-16 00:07:41 [scrapy.downloadermiddlewares.redirect] DEBUG: Redirecting (301) to  from 
User-Agent:Mozilla/5.0 (Windows NT 6.2) AppleWebKit/536.3 (KHTML, like Gecko) Chrome/19.0.1062.0 Safari/536.3

也可以把 user_agent_list放到 settings文件中去:

在rotate_useragent文件中加入一行代码

from randoms.settings import user_agent_list

运行效果如下:

完整的示例:http://download.csdn.net/detail/u011781521/9815390