一 。  去重的规则组件

去重数据，中通过set() 去重的， 留下的数据存在redis 中，

找到这个类  ： from scrapy.dupefilter import RFPDupeFilter

a. 爬虫中yield Request(...dont_filter=False)

b. 类

from scrapy.dupefilter import BaseDupeFilter

import redis

from scrapy.utils.request import request_fingerprint

class XzxDupefilter(BaseDupeFilter):

def __init__(self,key):

self.conn = None

self.key = key

@classmethod

def from_settings(cls, settings):

key = settings.get('DUP_REDIS_KEY')

return cls(key)

def open(self):

self.conn = redis.Redis(host='127.0.0.1',port=6379)

def request_seen(self, request):

fp = request_fingerprint(request)

added = self.conn.sadd(self.key, fp)

return added == 0

c. settings中配置

# 默认dupefilter

# DUPEFILTER_CLASS = 'scrapy.dupefilter.RFPDupeFilter'

DUPEFILTER_CLASS = 'xzx.dupfilter.XzxDupefilter' # 可以自定义的

这个类给url 添加一个唯一的标识：

from scrapy.utils.request import request_fingerprint

补充：调度器中有一段代码来规定

def enqueue_request(self, request):

# dont_filter=True, => False -> 添加到去重规则：False，True

# dont_filter=False, => True -> 添加到去重规则： False，True

if not request.dont_filter and self.df.request_seen(request):

return False

# 添加到调度器

dqok = self._dqpush(request)

二 。调度器

1. 广度优先 (本质就是栈)

2.深度优先 (本质就是队列)

3. 优先级队列 (redis的有序集合)

三  下载中间件

这个中间件事 调度器 于 下载器之间的中间件。

a. 　　　　scrapy中下载中间件的作用？

统一对所有请求批量对request对象进行下载前的预处理。

b. 针对user-agent，默认中间件 内置的默认的执行， 获取的是stettings 中自己配置的user-agent

class UserAgentMiddleware(object):

"""This middleware allows spiders to override the user_agent"""

def __init__(self, user_agent='Scrapy'):

self.user_agent = user_agent # USER_AGENT = 'Mozilla/5.0 (Windows NT 6.1; WOW64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/67.0.3396.99 Safari/537.36'

@classmethod

def from_crawler(cls, crawler):

o = cls(crawler.settings['USER_AGENT'])

crawler.signals.connect(o.spider_opened, signal=signals.spider_opened)

return o

def spider_opened(self, spider):

self.user_agent = getattr(spider, 'user_agent', self.user_agent)

def process_request(self, request, spider):

if self.user_agent:

request.headers.setdefault(b'User-Agent', self.user_agent)

c. 关于重定向 内置对的默认的

class BaseRedirectMiddleware(object):

enabled_setting = 'REDIRECT_ENABLED'

def __init__(self, settings):

if not settings.getbool(self.enabled_setting):

raise NotConfigured

self.max_redirect_times = settings.getint('REDIRECT_MAX_TIMES')

self.priority_adjust = settings.getint('REDIRECT_PRIORITY_ADJUST')

@classmethod

def from_crawler(cls, crawler):

return cls(crawler.settings)

def _redirect(self, redirected, request, spider, reason):

ttl = request.meta.setdefault('redirect_ttl', self.max_redirect_times)

redirects = request.meta.get('redirect_times', 0) + 1

if ttl and redirects <= self.max_redirect_times:

redirected.meta['redirect_times'] = redirects

redirected.meta['redirect_ttl'] = ttl - 1

redirected.meta['redirect_urls'] = request.meta.get('redirect_urls', []) + \

[request.url]

redirected.dont_filter = request.dont_filter

redirected.priority = request.priority + self.priority_adjust

logger.debug("Redirecting (%(reason)s) to %(redirected)s from %(request)s",

{'reason': reason, 'redirected': redirected, 'request': request},

extra={'spider': spider})

return redirected

else:

logger.debug("Discarding %(request)s: max redirections reached",

{'request': request}, extra={'spider': spider})

raise IgnoreRequest("max redirections reached")

def _redirect_request_using_get(self, request, redirect_url):

redirected = request.replace(url=redirect_url, method='GET', body='')

redirected.headers.pop('Content-Type', None)

redirected.headers.pop('Content-Length', None)

return redirected

class RedirectMiddleware(BaseRedirectMiddleware):

"""

Handle redirection of requests based on response status

and meta-refresh html tag.

"""

def process_response(self, request, response, spider):

if (request.meta.get('dont_redirect', False) or

response.status in getattr(spider, 'handle_httpstatus_list', []) or

response.status in request.meta.get('handle_httpstatus_list', []) or

request.meta.get('handle_httpstatus_all', False)):

return response

allowed_status = (301, 302, 303, 307, 308)

if 'Location' not in response.headers or response.status not in allowed_status:

return response

location = safe_url_string(response.headers['location'])

redirected_url = urljoin(request.url, location)

if response.status in (301, 307, 308) or request.method == 'HEAD':

redirected = request.replace(url=redirected_url)

return self._redirect(redirected, request, spider, response.status)

redirected = self._redirect_request_using_get(request, redirected_url)

return self._redirect(redirected, request, spider, response.status)

d. 关于cookie 是内置的默认的就执行

用法 自己写的逻辑里 yield 加上meta={“cookieJar”:1}}：

def start_requests(self):

for url in self.start_urls:

yield Request(url=url,callback=self.parse,meta={"cookieJar":1})

class CookiesMiddleware(object):

"""This middleware enables working with sites that need cookies"""

def __init__(self, debug=False):

self.jars = defaultdict(CookieJar)

self.debug = debug

@classmethod

def from_crawler(cls, crawler):

if not crawler.settings.getbool('COOKIES_ENABLED'):

raise NotConfigured

return cls(crawler.settings.getbool('COOKIES_DEBUG'))

def process_request(self, request, spider):

if request.meta.get('dont_merge_cookies', False):

return

# cookiejarkey = 1

cookiejarkey = request.meta.get("cookiejar")

jar = self.jars[cookiejarkey] # CookieJar对象-> 空容器

cookies = self._get_request_cookies(jar, request)

for cookie in cookies:

jar.set_cookie_if_ok(cookie, request)

# set Cookie header

request.headers.pop('Cookie', None)

jar.add_cookie_header(request)

self._debug_cookie(request, spider)

def process_response(self, request, response, spider):

if request.meta.get('dont_merge_cookies', False):

return response

# extract cookies from Set-Cookie and drop invalid/expired cookies

cookiejarkey = request.meta.get("cookiejar")

jar = self.jars[cookiejarkey]

jar.extract_cookies(response, request)

self._debug_set_cookie(response, spider)

return response

def _debug_cookie(self, request, spider):

if self.debug:

cl = [to_native_str(c, errors='replace')

for c in request.headers.getlist('Cookie')]

if cl:

cookies = "\n".join("Cookie: {}\n".format(c) for c in cl)

msg = "Sending cookies to: {}\n{}".format(request, cookies)

logger.debug(msg, extra={'spider': spider})

def _debug_set_cookie(self, response, spider):

if self.debug:

cl = [to_native_str(c, errors='replace')

for c in response.headers.getlist('Set-Cookie')]

if cl:

cookies = "\n".join("Set-Cookie: {}\n".format(c) for c in cl)

msg = "Received cookies from: {}\n{}".format(response, cookies)

logger.debug(msg, extra={'spider': spider})

def _format_cookie(self, cookie):

# build cookie string

cookie_str = '%s=%s' % (cookie['name'], cookie['value'])

if cookie.get('path', None):

cookie_str += '; Path=%s' % cookie['path']

if cookie.get('domain', None):

cookie_str += '; Domain=%s' % cookie['domain']

return cookie_str

def _get_request_cookies(self, jar, request):

if isinstance(request.cookies, dict):

cookie_list = [{'name': k, 'value': v} for k, v in \

six.iteritems(request.cookies)]

else:

cookie_list = request.cookies

cookies = [self._format_cookie(x) for x in cookie_list]

headers = {'Set-Cookie': cookies}

response = Response(request.url, headers=headers)

return jar.make_cookies(response, request)

默认中间件：

DOWNLOADER_MIDDLEWARES_BASE = {

# Engine side

'scrapy.downloadermiddlewares.robotstxt.RobotsTxtMiddleware': 100,

'scrapy.downloadermiddlewares.httpauth.HttpAuthMiddleware': 300,

'scrapy.downloadermiddlewares.downloadtimeout.DownloadTimeoutMiddleware': 350,

'scrapy.downloadermiddlewares.defaultheaders.DefaultHeadersMiddleware': 400,

'scrapy.downloadermiddlewares.useragent.UserAgentMiddleware': 500,

'scrapy.downloadermiddlewares.retry.RetryMiddleware': 550,

'scrapy.downloadermiddlewares.ajaxcrawl.AjaxCrawlMiddleware': 560,

'scrapy.downloadermiddlewares.redirect.MetaRefreshMiddleware': 580,

'scrapy.downloadermiddlewares.httpcompression.HttpCompressionMiddleware': 590,

'scrapy.downloadermiddlewares.redirect.RedirectMiddleware': 600,

'scrapy.downloadermiddlewares.cookies.CookiesMiddleware': 700,

'scrapy.downloadermiddlewares.httpproxy.HttpProxyMiddleware': 750,

'scrapy.downloadermiddlewares.stats.DownloaderStats': 850,

'scrapy.downloadermiddlewares.httpcache.HttpCacheMiddleware': 900,

# Downloader side

}

注意点：

process_request   不用返回，

1. 如果 有返回response，就会找最后一个process—ressponse

2. 如果返回request ， 就到直接根据返回的request 到调度器中执行

process_response:必须有返回值

四  。 爬虫中间件

下载器组件 到 爬虫组件中间件，

默认有 优先级的中间件 和 深度的中间件

编写中间件

class XzxSpiderMiddleware(object):

# Not all methods need to be defined. If a method is not defined,

# scrapy acts as if the spider middleware does not modify the

# passed objects.

@classmethod

def from_crawler(cls, crawler):

# This method is used by Scrapy to create your spiders.

s = cls()

return s

def process_spider_input(self, response, spider):

# Called for each response that goes through the spider

# middleware and into the spider.

# Should return None or raise an exception.

return None

def process_spider_output(self, response, result, spider):

# Called with the results returned from the Spider, after

# it has processed the response.

# Must return an iterable of Request, dict or Item objects.

for i in result:

yield i

def process_spider_exception(self, response, exception, spider):

# Called when a spider or process_spider_input() method

# (from other spider middleware) raises an exception.

# Should return either None or an iterable of Response, dict

# or Item objects.

pass

def process_start_requests(self, start_requests, spider):

# Called with the start requests of the spider, and works

# similarly to the process_spider_output() method, except

# that it doesn’t have a response associated.

# Must return only requests (not items).

for r in start_requests:

yield r

配置文件：

SPIDER_MIDDLEWARES = {

'xzx.middlewares.XzxSpiderMiddleware': 543,

}

内置爬虫中间件 settings 中的配置 ：

深度 ：

DEPTH_LIMIT = 8

优先级

DEPTH_PRIORITY = 1， 请求的优先级：0 -1 -2 -3 。。。。

DEPTH_PRIORITY = -1，请求的优先级：0 1 2 3 。。。。

SPIDER_MIDDLEWARES_BASE = {

# Engine side

'scrapy.spidermiddlewares.httperror.HttpErrorMiddleware': 50,

'scrapy.spidermiddlewares.offsite.OffsiteMiddleware': 500,

'scrapy.spidermiddlewares.referer.RefererMiddleware': 700,

'scrapy.spidermiddlewares.urllength.UrlLengthMiddleware': 800,

'scrapy.spidermiddlewares.depth.DepthMiddleware': 900,

# Spider side

}

总结：

1. DupeFilter

- 默认放在set集合

- url变更为唯一标记

- 将去重规则放到redis中的意义何在？

- 去重+dont_filter

2. 调度器

- 爬虫中什么是深度和广度优先？

- 用什么可以实现？

- 栈

- 队列

- 优先级集合

3，开放封闭原则：

对源码封闭，对配置文件开放， 通过修改配置文件，实现自己想要的功能.