python---Scrapy模块的使用（二）

出处：http://www.cnblogs.com/wupeiqi/

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(cls, settings):
        """
        初始化时，调用,
        :param settings:
        :return:
        """
        return cls()

    def request_seen(self, request):
        """
        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
        """
        print('.......')
        if request.url in self.visited_url:
            return True
        self.visited_url.add(request.url)
        return False

    def open(self):
        """
        开始爬去请求时，调用
        :return:
        """
        print('open')

    def close(self, reason):
        """
        结束爬虫爬取时，调用
        :param reason:
        :return:
        """
        print('close')

    def log(self, request, spider):
        """
        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

class ScrapyproPipeline(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(cls,crawler):
        '''
        初始化时候，用于创建pipeline对象,读取配置文件
        :param crawler: crawler.settings是在初始化时候就将配置文件放入crawler中了
        :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

    def open_spider(self,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(self, item, spider):
        '''
        每当数据需要持久化时，就会被调用，spider是爬虫对象
        :param item:
        :param spider:
        :return:
        '''

　　　　 if spider.name != "xiaohua":    #若是爬虫不符合，不进行持久化处理
    　　　　return item

        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()

    def close_spider(self,spider):
　　     '''爬虫关闭时执行'''
        print("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': ,
   'scrapyPro.pipelines.XiaohuaPipeline': ,  #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
        self.cookie_dict = 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":"", "message":"", "data":{"complateReg":"","destJid":"cdu_52941024478"}}}
        ret = json.loads(response.text,encoding="utf-8")
        if ret['result'].get("code") == "":
            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

DEPTH_LIMIT = 

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":
}

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

    @classmethod
    def from_crawler(cls, crawler):
        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

# . 爬虫名称
BOT_NAME = 'step8_king'

# . 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
# . 客户端 user-agent请求头 可伪造
# USER_AGENT = 'step8_king (+http://www.yourdomain.com)'

# Obey robots.txt rules
# . 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: )
# . 并发请求数
# CONCURRENT_REQUESTS = 

# Configure a delay for requests for the same website (default: )
# See http://scrapy.readthedocs.org/en/latest/topics/settings.html#download-delay
# See also autothrottle settings and docs
# . 延迟下载秒数
# DOWNLOAD_DELAY = 

# The download delay setting will honor only one of:
# . 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 =
# 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 = 

# Disable cookies (enabled by default)
# . 是否支持cookie，cookiejar进行操作cookie
# COOKIES_ENABLED = True
# COOKIES_DEBUG = True

# Disable Telnet Console (enabled by default)
# . 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 = [,]

# . 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
# . 定义pipeline处理请求
# ITEM_PIPELINES = {
#    'step8_king.pipelines.JsonPipeline': ,
#    'step8_king.pipelines.FilePipeline': ,
# }

# . 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': ,
# }

# . 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 = 

# . 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 =
# SCHEDULER_DISK_QUEUE = 'scrapy.squeue.PickleLifoDiskQueue'
# SCHEDULER_MEMORY_QUEUE = 'scrapy.squeue.LifoMemoryQueue'
# 先进先出，广度优先

# DEPTH_PRIORITY =
# SCHEDULER_DISK_QUEUE = 'scrapy.squeue.PickleFifoDiskQueue'
# SCHEDULER_MEMORY_QUEUE = 'scrapy.squeue.FifoMemoryQueue'

# . 调度器队列
# SCHEDULER = 'scrapy.core.scheduler.Scheduler'
# from scrapy.core.scheduler import Scheduler

# . 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

"""
. 自动限速算法
    from scrapy.contrib.throttle import AutoThrottle
    自动限速设置
    . 获取最小延迟 DOWNLOAD_DELAY
    . 获取最大延迟 AUTOTHROTTLE_MAX_DELAY
    . 设置初始下载延迟 AUTOTHROTTLE_START_DELAY
    . 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
    . 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 =
# The maximum download delay to be set in case of high latencies
# 最大下载延迟
# AUTOTHROTTLE_MAX_DELAY =
# 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

"""
. 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 = 

# 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'

"""
. 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': ,
    }

"""

"""
. Https访问
    Https访问时有两种情况：
    . 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"

    . 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

"""

"""
. 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': ,
        'scrapy.contrib.spidermiddleware.offsite.OffsiteMiddleware': ,
        'scrapy.contrib.spidermiddleware.referer.RefererMiddleware': ,
        'scrapy.contrib.spidermiddleware.urllength.UrlLengthMiddleware': ,
        'scrapy.contrib.spidermiddleware.depth.DepthMiddleware': ,

"""
# 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': ,
}

"""
. 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': ,
        'scrapy.contrib.downloadermiddleware.httpauth.HttpAuthMiddleware': ,
        'scrapy.contrib.downloadermiddleware.downloadtimeout.DownloadTimeoutMiddleware': ,
        'scrapy.contrib.downloadermiddleware.useragent.UserAgentMiddleware': ,
        'scrapy.contrib.downloadermiddleware.retry.RetryMiddleware': ,
        'scrapy.contrib.downloadermiddleware.defaultheaders.DefaultHeadersMiddleware': ,
        'scrapy.contrib.downloadermiddleware.redirect.MetaRefreshMiddleware': ,
        'scrapy.contrib.downloadermiddleware.httpcompression.HttpCompressionMiddleware': ,
        'scrapy.contrib.downloadermiddleware.redirect.RedirectMiddleware': ,
        'scrapy.contrib.downloadermiddleware.cookies.CookiesMiddleware': ,
        'scrapy.contrib.downloadermiddleware.httpproxy.HttpProxyMiddleware': ,
        'scrapy.contrib.downloadermiddleware.chunked.ChunkedTransferMiddleware': ,
        'scrapy.contrib.downloadermiddleware.stats.DownloaderStats': ,
        'scrapy.contrib.downloadermiddleware.httpcache.HttpCacheMiddleware': ,
    }

"""
# 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': ,
#    'step8_king.middlewares.DownMiddleware2': ,
# }

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

.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()

.在settings.py 中添加配置 COMMANDS_MODULE = '项目名称.目录名称'

.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