一：去除重复URL
scrapy默认使用 scrapy.dupefilter.RFPDupeFilter 进行去重，相关配置有：
DUPEFILTER_CLASS = ' scrapy.dupefilter.RFPDupeFilter '
DUPEFILTER_DEBUG = False
JOBDIR = " 保存范文记录的日志路径，如：/root/ " # 最终路径为 /root/requests.seen
下面自定义ULR去重操作：（将原来在spider中的操作分解开来）
duplication.py
class RepeatDupeFilter(object ):
def __init__(self):
self.visited_url = set ()
@classmethod
def from_settings """
初始化时，调用,
:param settings:
: return :
"""
return cls()
def request_seen """
检测当前请求是否已经被访问过
:param request:
: return : True表示已经访问过；False表示未访问过
""" if request.url in self.visited_url:
return True
self.visited_url.add(request.url)
return False
def open """
开始爬去请求时，调用
: return :
"""
print(' open ' )
def close """
结束爬虫爬取时，调用
:param reason:
: return :
"""
print(' close ' )
def log """
记录日志
:param request:
:param spider:
: return :
"""
print(' repeat ' , request.url)
settings.py
DUPEFILTER_CLASS = " scrapyPro.duplication.RepeatDupeFilter "
执行时机：会在引擎启动后开始执行，当对第一个url进行获取时，就会去调用该去重机制 二：pipeline补充
pipeline中不止可以解析数据，还可以进行其他扩展
pipelines.py
from scrapy.exceptions import DropItem object ):
def __init__(self,conn_str):
self.conn_str = conn_str
self.conn = None #数据库连接
print( " connect db " )
@classmethod
def from_crawler '''
初始化时候，用于创建pipeline对象,读取配置文件
:param crawler: crawler.settings
:return :
'''
conn_str = crawler.settings.get("DB" ) #获取数据库信息 #模拟数据库记录操作
print(" get db info " )
return cls(conn_str) #返回该对象，会去执行init方法 open_spider '''
每当爬虫开始执行的时候，调用
:param spider:
: return :
'''
# self.conn.open()
print( " chouti spider start " )
def process_item '''
每当数据需要持久化时，就会被调用，spider是爬虫对象 return :
''' if spider.name != "xiaohua": #若是爬虫不符合，不进行持久化处理
tpl = " %s\n%s\n\n " %(item[' href ' ],item[' title ' ])
with open( " news.josn " ,' a ' ) as fp:
fp.write(tpl)
#交给下一个pipeline处理
return item #和settings文件有关，当settings文件设置多个pipeline时，会依次去执行，若是不想执行可以丢弃item，不继续
#抛出异常DropItem表示终止，丢弃item，不交给下一个处理
# return DropItem() close_spider " chouti spilder close " )
# self.conn.close()
settings.py相关
ITEM_PIPELINES = { #每一个spider都会经过下面所有的pipeline，我们可以根据参数spider对象对其进行处理，也可以设置是否返回item，来设置是否继续向下执行
' scrapyPro.pipelines.ScrapyproPipeline ' : 300 ,
' scrapyPro.pipelines.XiaohuaPipeline ' : 100 , #后面小的优先
}
执行时机：会在上面的url去重后，获取完数据后，对数据进行持久化操作
补充：crawler.settings.get("DB")
我们可以在from_crawler的参数crawler中获取配置文件信息
使用crawler.settings. get (" DB " )
注意：我们在配置文件中键值设置中键必须是大写的
三：cookies获取，CookieJar
获取响应response的响应cookies
from scrapy.http.cookies import CookieJar
def parse(self, response):
#获取cookies
cookie_obj = CookieJar()
cookie_obj.extract_cookies(response,response.request) #从响应体中提取出cookies cookie_obj._cookies #注意cookies保存在cookiejar对象中的_cookies中
cookies实例：登录抽屉，实现点赞
import scrapy,hashlib,json
from scrapy.selector import Selector,HtmlXPathSelector
from scrapy.http import Request
from scrapy.http.cookies import CookieJar
class ChoutiSpider(scrapy.Spider):
name = ' chouti '
allowed_domains = [' chouti.com ' ]
start_urls = [' https://dig.chouti.com/ ' ]
cookie_dict = None
def parse(self, response):
#到首页，获取cookie
cookie_obj = CookieJar()
cookie_obj.extract_cookies(response,response.request)
self.cookie_dict = cookie_obj._cookies
yield Request(url=" https://dig.chouti.com/login " ,
cookies =self.cookie_dict,
method =" post " ,
headers ={
' user-agent ' :' Mozilla/5.0 (Windows NT 6.1; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/60.0.3112.90 Safari/537.36 ' ,
' content-type ' :' application/x-www-form-urlencoded; charset=UTF-8 '
},
body = " phone=账号&password=密码&oneMonth=1 " ,
callback =self.check_login
)
def check_login(self,response):
# print(response.text) #{ " result " :{" code " :" 9999 " , " message " :"" , " data " :{" complateReg " :" 0 " ," destJid " :" cdu_52941024478 " }}}
ret = json.loads(response.text,encoding=" utf-8 " )
if ret[' result ' ].get (" code " ) == " 9999 " :
yield Request(url=" https://dig.chouti.com/ " ,callback=self.favor)
def favor(self,response):
news_list = Selector(response=response).xpath(" //div[@class='part2']/@share-linkid " ).extract()
for news_id in news_list:
new_url = " https://dig.chouti.com/link/vote?linksId=%s " %news_id
yield Request(url=new_url,
method =" post " ,
headers ={
' user-agent ' : ' Mozilla/5.0 (Windows NT 6.1; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/60.0.3112.90 Safari/537.36 ' ,
' content-type ' : ' application/x-www-form-urlencoded; charset=UTF-8 '
},
cookies =self.cookie_dict, #正好凑巧，抽屉登录后的操作需要使用登录前的一个cookie值，我们没有在check_login中更新cookies_dict,所以纯属巧合
callback =self.show
)
page_list = Selector(response=response).xpath(" //a[@class='ct_pagepa']/@href " ).extract()
for page_url in page_list:
new_page_url = " https://dig.chouti.com%s " %page_url
yield Request(
url =new_page_url,
method =" get " ,
callback =self.favor
)
def show(self,response):
print(response.text)
注意：当我们无法进入show回调时，可能在settings中的深度设置太低
四：scrapy框架扩展，实现信号回调
自定义扩展时，利用信号在指定位置注册制定操作
在settings.py文件中设置扩展
EXTENSIONS = {
# ' scrapy.extensions.telnet.TelnetConsole ' : None, #None代表不执行
" scrapyPro.extensions.MyExtend " :100
}
扩展文件extensions.py
from scrapy import signals
class MyExtend:
def __init__(self, crawler):
self.crawler = crawler
#在指定信号上注册操作 crawler.signals.connect(self.start,signals.engine_started) #在引擎前端时调用我们定义的方法 return cls(crawler)
def start(self):
print( " extensions start " )
所有信号
engine_started = object ()
engine_stopped = object ()
spider_opened = object ()
spider_idle = object ()
spider_closed = object ()
spider_error = object ()
request_scheduled = object ()
request_dropped = object ()
response_received = object ()
response_downloaded = object ()
item_scraped = object ()
item_dropped = object ()
# for backwards compatibility
stats_spider_opened = spider_opened
stats_spider_closing = spider_closed
stats_spider_closed = spider_closed
item_passed = item_scraped
request_received = request_scheduled
执行时机：会在信号触发时，去执行相关方法 五：配置文件介绍
# 1 . 爬虫名称
BOT_NAME = ' step8_king '
# 2 . 爬虫应用路径
SPIDER_MODULES = [' step8_king.spiders ' ]
NEWSPIDER_MODULE = ' step8_king.spiders '
# Crawl responsibly by identifying yourself (and your website) on the user -agent
# 3 . 客户端 user-agent请求头 可伪造
# USER_AGENT = ' step8_king (+http://www.yourdomain.com) '
# Obey robots.txt rules
# 4 . 禁止爬虫原来配置（默认true，符合爬虫规则，人家不让就不去爬取）
# ROBOTSTXT_OBEY = False
# Configure maximum concurrent requests performed by Scrapy ( default : 16 )
# 5 . 并发请求数
# CONCURRENT_REQUESTS = 4
# 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
# 6 . 延迟下载秒数
# DOWNLOAD_DELAY = 2
# The download delay setting will honor only one of:
# 7 . 单域名访问并发数，并且延迟下次秒数也应用在每个域名
# CONCURRENT_REQUESTS_PER_DOMAIN = 2
# 单IP访问并发数，如果有值则忽略：CONCURRENT_REQUESTS_PER_DOMAIN，并且延迟下次秒数也应用在每个IP
# CONCURRENT_REQUESTS_PER_IP = 3
# Disable cookies (enabled by default )
# 8 . 是否支持cookie，cookiejar进行操作cookie
# COOKIES_ENABLED = True
# COOKIES_DEBUG = True
# Disable Telnet Console (enabled by default )
# 9 . Telnet用于查看当前爬虫的信息，操作爬虫等...
# 使用telnet ip port ，然后通过命令操作
# TELNETCONSOLE_ENABLED = True
# TELNETCONSOLE_HOST = ' 127.0.0.1 '
# TELNETCONSOLE_PORT = [6023 ,]
# 10 . 默认请求头
# 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 ' ,
# }
# Configure item pipelines
# See http: // scrapy.readthedocs.org/en/latest/topics/item-pipeline.html
# 11 . 定义pipeline处理请求
# ITEM_PIPELINES = {
# ' step8_king.pipelines.JsonPipeline ' : 700 ,
# ' step8_king.pipelines.FilePipeline ' : 500 ,
# }
# 12 . 自定义扩展，基于信号进行调用
# Enable or disable extensions
# See http: // scrapy.readthedocs.org/en/latest/topics/extensions.html
# EXTENSIONS = {
# # ' step8_king.extensions.MyExtension ' : 500 ,
# }
# 13 . 爬虫允许的最大深度，可以通过meta查看当前深度；0表示无深度
# DEPTH_LIMIT = 3
# 14 . 爬取时，0表示深度优先Lifo(默认)；1表示广度优先FiFo
# 后进先出，深度优先
# DEPTH_PRIORITY = 0
# SCHEDULER_DISK_QUEUE = ' scrapy.squeue.PickleLifoDiskQueue '
# SCHEDULER_MEMORY_QUEUE = ' scrapy.squeue.LifoMemoryQueue '
# 先进先出，广度优先
# DEPTH_PRIORITY = 1
# SCHEDULER_DISK_QUEUE = ' scrapy.squeue.PickleFifoDiskQueue '
# SCHEDULER_MEMORY_QUEUE = ' scrapy.squeue.FifoMemoryQueue '
# 15 . 调度器队列
# SCHEDULER = ' scrapy.core.scheduler.Scheduler '
# from scrapy.core.scheduler import Scheduler
# 16 . 访问URL去重
# DUPEFILTER_CLASS = ' step8_king.duplication.RepeatUrl '
# Enable and configure the AutoThrottle extension (disabled by default )
# See http: // doc.scrapy.org/en/latest/topics/autothrottle.html
"""
17 . 自动限速算法
from scrapy.contrib.throttle import AutoThrottle
自动限速设置
1 . 获取最小延迟 DOWNLOAD_DELAY
2 . 获取最大延迟 AUTOTHROTTLE_MAX_DELAY
3 . 设置初始下载延迟 AUTOTHROTTLE_START_DELAY
4 . 当请求下载完成后，获取其" 连接 " 时间 latency，即：请求连接到接受到响应头之间的时间
5 . 用于计算的... AUTOTHROTTLE_TARGET_CONCURRENCY
target_delay = latency / self.target_concurrency
new_delay = (slot.delay + target_delay) / 2.0 # 表示上一次的延迟时间
new_delay = max(target_delay, new_delay)
new_delay = min(max(self.mindelay, new_delay), self.maxdelay)
slot.delay = new_delay
"""
# 开始自动限速
# AUTOTHROTTLE_ENABLED = True
# The initial download delay
# 初始下载延迟
# AUTOTHROTTLE_START_DELAY = 5
# The maximum download delay to be set in case of high latencies
# 最大下载延迟
# AUTOTHROTTLE_MAX_DELAY = 10
# The average number of requests Scrapy should be sending in parallel to each remote server
# 平均每秒并发数
# AUTOTHROTTLE_TARGET_CONCURRENCY = 1.0
# Enable showing throttling stats for every response received:
# 是否显示
# AUTOTHROTTLE_DEBUG = True
# Enable and configure HTTP caching (disabled by default )
# See http: // scrapy.readthedocs.org/en/latest/topics/downloader-middleware.html#httpcache-middleware-settings
"""
18 . 启用缓存
目的用于将已经发送的请求或相应缓存下来，以便以后使用
from scrapy.downloadermiddlewares.httpcache import HttpCacheMiddleware
from scrapy.extensions.httpcache import DummyPolicy
from scrapy.extensions.httpcache import FilesystemCacheStorage
"""
# 是否启用缓存策略
# HTTPCACHE_ENABLED = True
# 缓存策略：所有请求均缓存，下次在请求直接访问原来的缓存即可
# HTTPCACHE_POLICY = " scrapy.extensions.httpcache.DummyPolicy "
# 缓存策略：根据Http响应头：Cache -Control、Last-Modified 等进行缓存的策略
# HTTPCACHE_POLICY = " scrapy.extensions.httpcache.RFC2616Policy "
# 缓存超时时间
# HTTPCACHE_EXPIRATION_SECS = 0
# 缓存保存路径
# HTTPCACHE_DIR = ' httpcache '
# 缓存忽略的Http状态码
# HTTPCACHE_IGNORE_HTTP_CODES = []
# 缓存存储的插件
# HTTPCACHE_STORAGE = ' scrapy.extensions.httpcache.FilesystemCacheStorage '
"""
19 . 代理，需要在环境变量中设置
from scrapy.contrib.downloadermiddleware.httpproxy import HttpProxyMiddleware
方式一：使用默认
os.environ
{
http_proxy:http: // root:woshiniba@192.168.11.11:9999/
https_proxy:http:// 192.168.11.11:9999/
}
方式二：使用自定义下载中间件（推荐：灵活）
def to_bytes(text, encoding =None, errors=' strict ' ):
if isinstance(text, bytes):
return text
if not isinstance(text, six.string_types):
raise TypeError( ' to_bytes must receive a unicode, str or bytes '
' object, got %s ' % type(text).__name__)
if encoding is None:
encoding = ' utf-8 '
return text.encode(encoding, errors)
class ProxyMiddleware(object ):
def process_request(self, request, spider):
PROXIES = [
{ ' ip_port ' : ' 111.11.228.75:80 ' , ' user_pass ' : '' },
{ ' ip_port ' : ' 120.198.243.22:80 ' , ' user_pass ' : '' },
{ ' ip_port ' : ' 111.8.60.9:8123 ' , ' user_pass ' : '' },
{ ' ip_port ' : ' 101.71.27.120:80 ' , ' user_pass ' : '' },
{ ' ip_port ' : ' 122.96.59.104:80 ' , ' user_pass ' : '' },
{ ' ip_port ' : ' 122.224.249.122:8088 ' , ' user_pass ' : '' },
]
proxy = random.choice(PROXIES)
if proxy[' user_pass ' ] is not None:
request.meta[ ' proxy ' ] = to_bytes（" http://%s " % proxy[' ip_port ' ]）
encoded_user_pass = base64.encodestring(to_bytes(proxy[' user_pass ' ]))
request.headers[ ' Proxy-Authorization ' ] = to_bytes(' Basic ' + encoded_user_pass)
print " **************ProxyMiddleware have pass************ " + proxy[' ip_port ' ]
else :
print " **************ProxyMiddleware no pass************ " + proxy[' ip_port ' ]
request.meta[ ' proxy ' ] = to_bytes(" http://%s " % proxy[' ip_port ' ])
DOWNLOADER_MIDDLEWARES = {
' step8_king.middlewares.ProxyMiddleware ' : 500 ,
}
"""
"""
20 . Https访问
Https访问时有两种情况：
1 . 要爬取网站使用的可信任证书(默认支持)
DOWNLOADER_HTTPCLIENTFACTORY = " scrapy.core.downloader.webclient.ScrapyHTTPClientFactory "
DOWNLOADER_CLIENTCONTEXTFACTORY = " scrapy.core.downloader.contextfactory.ScrapyClientContextFactory "
2 . 要爬取网站使用的自定义证书
DOWNLOADER_HTTPCLIENTFACTORY = " scrapy.core.downloader.webclient.ScrapyHTTPClientFactory "
DOWNLOADER_CLIENTCONTEXTFACTORY = " step8_king.https.MySSLFactory "
# https.py
from scrapy.core.downloader.contextfactory import ScrapyClientContextFactory
from twisted.internet.ssl import (optionsForClientTLS, CertificateOptions, PrivateCertificate)
class MySSLFactory(ScrapyClientContextFactory):
def getCertificateOptions(self):
from OpenSSL import crypto
v1 = crypto.load_privatekey(crypto.FILETYPE_PEM, open(' /Users/wupeiqi/client.key.unsecure ' , mode=' r ' ).read())
v2 = crypto.load_certificate(crypto.FILETYPE_PEM, open(' /Users/wupeiqi/client.pem ' , mode=' r ' ).read())
return CertificateOptions(
privateKey =v1, # pKey对象
certificate =v2, # X509对象
verify =False,
method =getattr(self, ' method ' , getattr(self, ' _ssl_method ' , None))
)
其他：
相关类
scrapy.core.downloader.handlers.http.HttpDownloadHandler
scrapy.core.downloader.webclient.ScrapyHTTPClientFactory
scrapy.core.downloader.contextfactory.ScrapyClientContextFactory
相关配置
DOWNLOADER_HTTPCLIENTFACTORY
DOWNLOADER_CLIENTCONTEXTFACTORY
"""
"""
21 . 爬虫中间件
class SpiderMiddleware(object ):
def process_spider_input(self,response, spider):
'''
下载完成，执行，然后交给parse处理（在spider处理前）
:param response:
:param spider:
: return :
'''
pass
def process_spider_output(self,response, result, spider):
'''
spider处理完成，返回时调用（在spider处理后）
:param response:
:param result:
:param spider:
: return : 必须返回包含 Request 或 Item 对象的可迭代对象(iterable)
'''
return result
def process_spider_exception(self,response, exception, spider):
'''
异常调用
:param response:
:param exception:
:param spider:
: return : None,继续交给后续中间件处理异常；含 Response 或 Item 的可迭代对象(iterable)，交给调度器或pipeline
'''
return None
def process_start_requests(self,start_requests, spider):
'''
爬虫启动时调用,第一次使用时，针对start_url
:param start_requests:
:param spider:
: return : 包含 Request 对象的可迭代对象
'''
return start_requests
内置爬虫中间件：
' scrapy.contrib.spidermiddleware.httperror.HttpErrorMiddleware ' : 50 ,
' scrapy.contrib.spidermiddleware.offsite.OffsiteMiddleware ' : 500 ,
' scrapy.contrib.spidermiddleware.referer.RefererMiddleware ' : 700 ,
' scrapy.contrib.spidermiddleware.urllength.UrlLengthMiddleware ' : 800 ,
' scrapy.contrib.spidermiddleware.depth.DepthMiddleware ' : 900 ,
"""
# from scrapy.contrib.spidermiddleware.referer import RefererMiddleware
# Enable or disable spider middlewares
# See http: // scrapy.readthedocs.org/en/latest/topics/spider-middleware.html
SPIDER_MIDDLEWARES = {
# ' step8_king.middlewares.SpiderMiddleware ' : 543 ,
}
"""
22 . 下载中间件
class DownMiddleware1(object ):
def process_request(self, request, spider):
'''
请求需要被下载时，经过所有下载器中间件的process_request调用
:param request:
:param spider:
: return :
None,继续后续中间件去下载；
Response对象，停止process_request的执行，开始执行process_response
Request对象，停止中间件的执行，将Request重新调度器
raise IgnoreRequest异常，停止process_request的执行，开始执行process_exception
'''
pass
def process_response(self, request, response, spider):
'''
spider处理完成，返回时调用
:param response:
:param result:
:param spider:
: return :
Response 对象：转交给其他中间件process_response
Request 对象：停止中间件，request会被重新调度下载
raise IgnoreRequest 异常：调用Request.errback
'''
print(' response1 ' )
return response
def process_exception(self, request, exception, spider):
'''
当下载处理器(download handler)或 process_request() (下载中间件)抛出异常
:param response:
:param exception:
:param spider:
: return :
None：继续交给后续中间件处理异常；
Response对象：停止后续process_exception方法
Request对象：停止中间件，request将会被重新调用下载
'''
return None
默认下载中间件
{
' scrapy.contrib.downloadermiddleware.robotstxt.RobotsTxtMiddleware ' : 100 ,
' scrapy.contrib.downloadermiddleware.httpauth.HttpAuthMiddleware ' : 300 ,
' scrapy.contrib.downloadermiddleware.downloadtimeout.DownloadTimeoutMiddleware ' : 350 ,
' scrapy.contrib.downloadermiddleware.useragent.UserAgentMiddleware ' : 400 ,
' scrapy.contrib.downloadermiddleware.retry.RetryMiddleware ' : 500 ,
' scrapy.contrib.downloadermiddleware.defaultheaders.DefaultHeadersMiddleware ' : 550 ,
' scrapy.contrib.downloadermiddleware.redirect.MetaRefreshMiddleware ' : 580 ,
' scrapy.contrib.downloadermiddleware.httpcompression.HttpCompressionMiddleware ' : 590 ,
' scrapy.contrib.downloadermiddleware.redirect.RedirectMiddleware ' : 600 ,
' scrapy.contrib.downloadermiddleware.cookies.CookiesMiddleware ' : 700 ,
' scrapy.contrib.downloadermiddleware.httpproxy.HttpProxyMiddleware ' : 750 ,
' scrapy.contrib.downloadermiddleware.chunked.ChunkedTransferMiddleware ' : 830 ,
' scrapy.contrib.downloadermiddleware.stats.DownloaderStats ' : 850 ,
' scrapy.contrib.downloadermiddleware.httpcache.HttpCacheMiddleware ' : 900 ,
}
"""
# from scrapy.contrib.downloadermiddleware.httpauth import HttpAuthMiddleware
# Enable or disable downloader middlewares
# See http: // scrapy.readthedocs.org/en/latest/topics/downloader-middleware.html
# DOWNLOADER_MIDDLEWARES = {
# ' step8_king.middlewares.DownMiddleware1 ' : 100 ,
# ' step8_king.middlewares.DownMiddleware2 ' : 500 ,
# }
六：下载中间件和爬虫中间件
class SpiderMiddleware(object ):
def process_spider_input(self,response, spider):
"""
下载完成，执行，然后交给parse处理
:param response:
:param spider:
: return :
"""
pass
def process_spider_output(self,response, result, spider):
"""
spider处理完成，返回时调用
:param response:
:param result:
:param spider:
: return : 必须返回包含 Request 或 Item 对象的可迭代对象(iterable)
"""
return result
def process_spider_exception(self,response, exception, spider):
"""
异常调用
:param response:
:param exception:
:param spider:
: return : None,继续交给后续中间件处理异常；含 Response 或 Item 的可迭代对象(iterable)，交给调度器或pipeline
"""
return None
def process_start_requests(self,start_requests, spider):
"""
爬虫启动时调用
:param start_requests:
:param spider:
: return : 包含 Request 对象的可迭代对象
"""
return start_requests
爬虫中间件需要在settings中配置SPIDER_MIDDLEWARES
class DownMiddleware1(object ):
def process_request(self, request, spider):
"""
请求需要被下载时，经过所有下载器中间件的process_request调用
:param request:
:param spider:
: return :
None,继续后续中间件去下载；
Response对象，停止process_request的执行，开始执行process_response
Request对象，停止中间件的执行，将Request重新调度器
raise IgnoreRequest异常，停止process_request的执行，开始执行process_exception
"""
pass
def process_response(self, request, response, spider):
"""
spider处理完成，返回时调用
:param response:
:param result:
:param spider:
: return :
Response 对象：转交给其他中间件process_response
Request 对象：停止中间件，request会被重新调度下载
raise IgnoreRequest 异常：调用Request.errback
"""
print(' response1 ' )
return response
def process_exception(self, request, exception, spider):
"""
当下载处理器(download handler)或 process_request() (下载中间件)抛出异常
:param response:
:param exception:
:param spider:
: return :
None：继续交给后续中间件处理异常；
Response对象：停止后续process_exception方法
Request对象：停止中间件，request将会被重新调用下载
"""
return None
下载中间件需要在settings中配置DOWNLOADER_MIDDLEWARES 七：自定义命令
1.在spiders同级创建任意目录，如：commands
2 .在其中创建 crawlall.py 文件 （此处文件名就是自定义的命令）
from scrapy.commands import ScrapyCommand
from scrapy.utils.project import get_project_settings
class Command(ScrapyCommand):
requires_project = True
def syntax(self):
return ' [options] '
def short_desc(self):
return ' Runs all of the spiders '
def run(self, args, opts):
spider_list = self.crawler_process.spiders.list()
for name in spider_list:
self.crawler_process.crawl(name, **opts.__dict__)
self.crawler_process.start()
3 .在settings.py 中添加配置 COMMANDS_MODULE = ' 项目名称.目录名称 '
4 .在项目目录执行命令：scrapy crawlall
注意：自定制命令是我们研究爬虫源码的入口
