抓取到的item 会被发送到Item Pipeline进行处理
Item Pipeline常用于
- cleansing HTML data
- validating scraped data (checking that the items contain certain fields)
- checking for duplicates (and dropping them)
- storing the scraped item in a database
目录[隐藏] |
写一个自己的item pipeline
就是写一个Python类，并且实现process_item(item, spider)方法
must either return a Item (or any descendant子孙 class) object or raise a DropItem exception.
Price validation and dropping items with no prices
adjusts the price attribute for those items that do not include VAT (price_excludes_vat attribute), and drops those items which don’t contain a price:
如果没有price则丢掉，如果没有price_excludes_vat，调整价格值。
from scrapy.exceptions import DropItem class PricePipeline(object): vat_factor =1.15 def process_item(self, item, spider): if item['price']: if item['price_excludes_vat']: item['price']= item['price'] * self.vat_factor
return item else: raise DropItem("Missing price in %s" % item)
写到JSON文件中
import json class JsonWriterPipeline(object): def__init__(self): self.file=open('items.jl','wb') def process_item(self, item, spider): line = json.dumps(dict(item)) + " "
self.file.write(line)
return itemDuplicates filter
A filter that looks for duplicate items, and drops those items that were already processed. Let say that our items have an unique id, but our spider returns multiples items with the same id:
from scrapy.exceptionsimport DropItem class DuplicatesPipeline(object): def__init__(self): self.ids_seen=set() def process_item(self, item, spider): if item['id']in self.ids_seen: raise DropItem("Duplicate item found: %s" % item)
else: self.ids_seen.add(item['id'])
return itemActivating激活 an Item Pipeline component
在settings.py中加入如下代码：
ITEM_PIPELINES ={'myproject.pipelines.PricePipeline': 300,'myproject.pipelines.JsonWriterPipeline': 800,}
我们在Scrapy爬虫入门系列2:示例教程的基础上，支持json输出
- 1，先写好pipeline
import json class TutorialPipeline(object): def__init__(self): self.file=open('output.json','wb') def process_item(self, item, spider): line = json.dumps(dict(item)) + " "
self.file.write(line)
return item- 2，然后在settings.py中加入
ITEM_PIPELINES={'tutorial.pipelines.TutorialPipeline':400,}
最后运行scrapy crawl dmoz会生成output.json。
存入数据库
打开pipelines.py输入如下：
# -*- coding: utf-8 -*- # Define your item pipelines here
## Don't forget to add your pipeline to the ITEM_PIPELINES setting# See: http://doc.scrapy.org/en/latest/topics/item-pipeline.html # -*- coding: utf-8 -*-
from scrapy import log from twisted.enterprise import adbapi from scrapy.httpimport Request from scrapy.selectorimport HtmlXPathSelector import urllib import MySQLdb import MySQLdb.cursors class TutorialPipeline(object): def__init__(self): self.dbpool= adbapi.ConnectionPool('MySQLdb',db ='scrapy',user='root',passwd ='pwd', cursorclass = MySQLdb.cursors.DictCursor, charset ='utf8', use_unicode =False)
def process_item(self, item, spider): query =self.dbpool.runInteraction(self._conditional_insert, item) query.addErrback(self.handle_error)
return item def _conditional_insert(self,tx,item): tx.execute("select * from item where title = %s",(item['title'])) result=tx.fetchone()
# log.msg(result,level=log.DEBUG)#print result
if result: log.msg("Item already stored in db:%s" % item,level=log.DEBUG)
else: tx.execute("insert into item (title) values (%s)",(item['title']))
def handle_error(self, e): log.err(e)
请注意python的缩进，不然会报错。
然后在settings.py里加上：
ITEM_PIPELINES={'tutorial.pipelines.TutorialPipeline':400,}
运行scrapy crawl dmoz，会发现数据成功插入到数据库中：
如果报错：
No module named MySQLdb
解决：
yum install MySQL-python pip install mysql-python
源码下载：艺搜下载
[编辑]艺搜参考
http://doc.scrapy.org/en/latest/topics/item-pipeline.html
http://stackoverflow.com/questions/10845839/writing-items-to-a-mysql-database-in-scrapy