scrapy的扩展件extensions

extensions.py文件
 
# -*- coding: utf-8 -*-
# 该扩展会在以下事件时记录一条日志：
# spider被打开
# spider被关闭
# 爬取了特定数量的条目(items)

import logging
from collections import defaultdict
from scrapy import signals
from scrapy.exceptions import NotConfigured
from datetime import datetime
 
logger = logging.getLogger(__name__)
 
class SpiderOpenCloseLogging(object):
 
    def __init__(self, item_count):
        self.item_count = item_count
        self.items_scraped = 0
        self.items_dropped = 0
        self.stats = defaultdict(int)  # 默认是0   正常状态
        self.err_stats = defaultdict(int)  # 默认是0
        print("=="*20, 'Extension object created 扩展对象被创建')
 
    @classmethod
    def from_crawler(cls, crawler):
        # first check if the extension should be enabled and raise
 
        # NotConfigured otherwise
        # 关键：这里如果是False就直接放弃对象的创建了，在settings中写一个MYEXT_ENABLED，设置为True
        if not crawler.settings.getbool('MYEXT_ENABLED'):
            raise NotConfigured
 
        # get the number of items from settings
        # 默认每爬1000条才记录一次log，可以在settings中设置这个MYEXT_ITEMCOUNT数字
        item_count = crawler.settings.getint('MYEXT_ITEMCOUNT', 1000)
 
        # instantiate the extension object
 
        ext = cls(item_count)
 
        # connect the extension object to signals
        # 把ext.spider_opened这个函数绑定到signal=signals.spider_opened这个信号上，
        # 每当一个item对象被yield出来的时候，这个信号就会产生
        crawler.signals.connect(ext.spider_opened, signal=signals.spider_opened)
 
        crawler.signals.connect(ext.spider_closed, signal=signals.spider_closed)
 
        # signals.item_scraped这个是主要的信号，前提是一个item被爬之后，并通过所有的Pipeline没有被drop掉
        crawler.signals.connect(ext.item_scraped, signal=signals.item_scraped)
 
        # 注册一个item_dropped信号，当item被drop之后这个信号会触发
        crawler.signals.connect(ext.item_dropped, signal=signals.item_dropped)
 
        # 注册一个ext.response_received
        crawler.signals.connect(ext.response_received, signal=signals.response_received)
 
        # return the extension object
 
        return ext
 
    def spider_opened(self, spider):
        # spider.log("opened spider %s" % spider.name)
        # 可以把spider.log替换成print
        print("opened spider %s" % spider.name)
 
    def spider_closed(self, spider):
        # spider.log("closed spider %s" % spider.name)
        # 可以把spider.log替换成print
        print("closed spider %s" % spider.name)
 
    def item_scraped(self, item, spider):
        self.items_scraped += 1
        if self.items_scraped % self.item_count == 0:
            # spider.log("scraped %d items" % self.items_scraped)
            # 可以把spider.log替换成print
            print("scraped %d items" % self.items_scraped)
 
    def item_dropped(self, item, spider, response, exception):
        self.items_dropped += 1
        if self.items_dropped % self.item_count == 0:
            # spider.log("scraped %d items" % self.items_scraped)
            print("dropped %d items" % self.items_dropped)
 
    def response_received(self, response, request, spider):  # 监控爬虫的健康情况
        # 统计当前这一分钟正确状态和错误状态的数量
        now = datetime.now().strftime('%Y%m%d%H%M')
        self.stats[now] += 1  # 正常状态+！
        if response.status in [401, 403, 404, 500, 501, 502]:
            self.err_stats[now] += 1  # 错误状态+1
        if self.err_stats[now] / float(self.stats[now]) > 0.2:  # 占比
            # 一般线上部署有warning信息会发邮件，有err信息会发短信
            # warning级别比err低，但是比info高
            logger.warning(f'received {self.stats[now]} response and {self.err_stats[now]} of them is not 200，{now}')

settings中配置文件
 
# Enable or disable extensions
# See https://docs.scrapy.org/en/latest/topics/extensions.html
MYEXT_ENABLED = True  # 使用自定义插件
MYEXT_ITEMCOUNT = 10  # 每爬10条打印一次或者记录一次日志
EXTENSIONS = {
   # 'scrapy.extensions.telnet.TelnetConsole': None,
   'qianmu.extensions.SpiderOpenCloseLogging': 1,
}