python组件介绍_python 中的爬虫· scrapy框架 重要的组件的介绍
一 。? 去重的規則組件
去重數據，中通過set() 去重的， 留下的數據存在redis 中，
找到這個類? ： from scrapy.dupefilter import RFPDupeFilter
a. 爬蟲中yield Request(...dont_filter=False)
b. 類
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
# 默認dupefilter
# DUPEFILTER_CLASS = 'scrapy.dupefilter.RFPDupeFilter'
DUPEFILTER_CLASS = 'xzx.dupfilter.XzxDupefilter' # 可以自定義的
這個類給url 添加一個唯一的標識：
from scrapy.utils.request import request_fingerprint
補充：調度器中有一段代碼來規定
def enqueue_request(self, request):
# dont_filter=True, => False -> 添加到去重規則：False，True
# dont_filter=False, => True -> 添加到去重規則： False，True
if not request.dont_filter and self.df.request_seen(request):
return False
# 添加到調度器
dqok = self._dqpush(request)
二 。調度器
1. 廣度優先 (本質就是棧)
2.深度優先 (本質就是隊列)
3. 優先級隊列 (redis的有序集合)
三? 下載中間件
這個中間件事 調度器 于 下載器之間的中間件。
a. scrapy中下載中間件的作用？
統一對所有請求批量對request對象進行下載前的預處理。
b. 針對user-agent，默認中間件 內置的默認的執行， 獲取的是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. 關于重定向 內置對的默認的
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. 關于cookie 是內置的默認的就執行
用法 自己寫的邏輯里 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對象-> 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)
默認中間件：
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
}
注意點：
process_request? ?不用返回，
1.?如果 有返回response，就會找最后一個process—ressponse
2. 如果返回request ， 就到直接根據返回的request 到調度器中執行
process_response:必須有返回值
四? 。 爬蟲中間件
下載器組件 到 爬蟲組件中間件，
默認有 優先級的中間件 和 深度的中間件
編寫中間件
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,
}
內置爬蟲中間件 settings 中的配置 ：
深度 ：
DEPTH_LIMIT = 8
優先級
DEPTH_PRIORITY = 1， 請求的優先級：0 -1 -2 -3 。。。。
DEPTH_PRIORITY = -1，請求的優先級：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
}
總結：
1. DupeFilter
- 默認放在set集合
- url變更為唯一標記
- 將去重規則放到redis中的意義何在？
- 去重+dont_filter
2. 調度器
- 爬蟲中什么是深度和廣度優先？
- 用什么可以實現？
- 棧
- 隊列
- 優先級集合
3，開放封閉原則：
對源碼封閉，對配置文件開放， 通過修改配置文件，實現自己想要的功能.
總結
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