python - scrapy 项目在将它们存储到 couchdb 时不是 JSON 可序列化的

Question

items.py classes

import scrapy
from scrapy.item import Item, Field
import json


class Attributes(scrapy.Item):
    description = Field()
    pages=Field()
    author=Field()
class Vendor(scrapy.Item):
    title=Field()
    order_url=Field()

class bookItem(scrapy.Item):

    title = Field()
    url = Field()
    marketprice=Field()
    images=Field()
    price=Field()
    attributes=Field()
    vendor=Field()
    time_scraped=Field()

---

我的抓取工具

from scrapy.contrib.spiders import CrawlSpider, Rule
from scrapy.contrib.linkextractors.sgml import SgmlLinkExtractor
from scrapy.selector import HtmlXPathSelector
from scrapy.item import Item
from scrapy.spider import BaseSpider
from scrapy import log
from scrapper.items import bookItem,Attributes,Vendor
import couchdb
import logging
import json
import time
from couchdb import Server


class libertySpider(CrawlSpider):
   

    couch = couchdb.Server()
    db = couch['python-tests']
    name = "libertybooks"
    allowed_domains = ["libertybooks.com"]
    unvisited_urls = []
    visited_urls = []
    start_urls = [
        "http://www.libertybooks.com"
    ]
    url=["http://www.kaymu.pk"]
    rules = [Rule(SgmlLinkExtractor(),  callback='parse_item', follow=True)]
    
    total=0
    productpages=0
    exceptionnum=0



    def parse_item(self,response):
        if response.url.find("pid")!=-1:
            with open("number.html","w") as w:
                self.total=self.total+1
                w.write(str(self.total)+","+str(self.productpages))
            itm=bookItem()
            attrib=Attributes()
            ven=Vendor()
            images=[]
            try:
                name=response.xpath('//span[@id="pagecontent_lblbookName"]/text()').extract()[0]
                name=name.encode('utf-8')
                
            except:
                name="name not found"
            try:
                price=response.xpath('//span[@id="pagecontent_lblPrice"]/text()').extract()[0]
                price=price.encode('utf-8')
            except:
                price=-1
            try:
                marketprice=response.xpath('//span[@id="pagecontent_lblmarketprice"]/text()').extract()[0]
                marketprice=marketprice.encode('utf-8')
            except:
                marketprice=-1
            try:
                pages=response.xpath('//span[@id="pagecontent_spanpages"]/text()').extract()[0]
                pages=pages.encode('utf-8')
            except:
                pages=-1
            try:
                author=response.xpath('//span[@id="pagecontent_lblAuthor"]/text()').extract()[0]
                author=author.encode('utf-8')
            except:
                author="author not found"
            try:
                description=response.xpath('//span[@id="pagecontent_lblbookdetail"]/text()').extract()[0]
                description=description.encode('utf-8')
            except:
                description="des: not found"
            try:
                image=response.xpath('//img[@id="pagecontent_imgProduct"]/@src').extract()[0]
                image=image.encode('utf-8')
            except:
                image="#"


            ven['title']='libertybooks'
            ven['order_url']=response.url
            itm['vendor']=ven
           
            itm['time_scraped']=time.ctime()
            



            itm['title']=name
            itm['url']=response.url




            itm['price']=price
            itm['marketprice']=marketprice
            itm['images']=images

            attrib['pages']=pages
            attrib['author']=author
            attrib['description']=description
            itm['attributes']=attrib
 
            self.saveindb(itm)
            return itm

    def saveindb(self,obj):
        logging.debug(obj)
        self.db.save(obj)

---

堆栈跟踪

2014-12-09 13:57:37-0800 [libertybooks] ERROR: Spider error processing <GET http://www.libertybooks.com/bookdetail.aspx?pid=16532>
    Traceback (most recent call last):
      File "/usr/lib/python2.7/dist-packages/twisted/internet/base.py", line 824, in runUntilCurrent
        call.func(*call.args, **call.kw)
      File "/usr/lib/python2.7/dist-packages/twisted/internet/task.py", line 638, in _tick
        taskObj._oneWorkUnit()
      File "/usr/lib/python2.7/dist-packages/twisted/internet/task.py", line 484, in _oneWorkUnit
        result = next(self._iterator)
      File "/usr/local/lib/python2.7/dist-packages/scrapy/utils/defer.py", line 57, in <genexpr>
        work = (callable(elem, *args, **named) for elem in iterable)
    --- <exception caught here> ---
      File "/usr/local/lib/python2.7/dist-packages/scrapy/utils/defer.py", line 96, in iter_errback
        yield next(it)
      File "/usr/local/lib/python2.7/dist-packages/scrapy/contrib/spidermiddleware/offsite.py", line 26, in process_spider_output
        for x in result:
      File "/usr/local/lib/python2.7/dist-packages/scrapy/contrib/spidermiddleware/referer.py", line 22, in <genexpr>
        return (_set_referer(r) for r in result or ())
      File "/usr/local/lib/python2.7/dist-packages/scrapy/contrib/spidermiddleware/urllength.py", line 33, in <genexpr>
        return (r for r in result or () if _filter(r))
      File "/usr/local/lib/python2.7/dist-packages/scrapy/contrib/spidermiddleware/depth.py", line 50, in <genexpr>
        return (r for r in result or () if _filter(r))
      File "/usr/local/lib/python2.7/dist-packages/scrapy/contrib/spiders/crawl.py", line 67, in _parse_response
        cb_res = callback(response, **cb_kwargs) or ()
      File "/home/asad/Desktop/scraper/scraper/spiders/liberty_spider.py", line 107, in parse_item
        self.saveindb(itm)
      File "/home/asad/Desktop/scraper/scraper/spiders/liberty_spider.py", line 112, in saveindb
        self.db.save(obj)
      File "/usr/local/lib/python2.7/dist-packages/couchdb/client.py", line 431, in save
        _, _, data = func(body=doc, **options)
      File "/usr/local/lib/python2.7/dist-packages/couchdb/http.py", line 514, in post_json
        **params)
      File "/usr/local/lib/python2.7/dist-packages/couchdb/http.py", line 533, in _request_json
        headers=headers, **params)
      File "/usr/local/lib/python2.7/dist-packages/couchdb/http.py", line 529, in _request
        credentials=self.credentials)
      File "/usr/local/lib/python2.7/dist-packages/couchdb/http.py", line 244, in request
        body = json.encode(body).encode('utf-8')
      File "/usr/local/lib/python2.7/dist-packages/couchdb/json.py", line 69, in encode
        return _encode(obj)
      File "/usr/local/lib/python2.7/dist-packages/couchdb/json.py", line 135, in <lambda>
        dumps(obj, allow_nan=False, ensure_ascii=False)
      File "/usr/lib/python2.7/json/__init__.py", line 250, in dumps
        sort_keys=sort_keys, **kw).encode(obj)
      File "/usr/lib/python2.7/json/encoder.py", line 207, in encode
        chunks = self.iterencode(o, _one_shot=True)
      File "/usr/lib/python2.7/json/encoder.py", line 270, in iterencode
        return _iterencode(o, 0)
      File "/usr/lib/python2.7/json/encoder.py", line 184, in default
        raise TypeError(repr(o) + " is not JSON serializable")
    exceptions.TypeError: {'attributes': {'author': 'Tina Fey',
     'description': "Once in a generation a woman comes along who changes everything. Tina Fey is not that woman, but she met that woman once and acted weird around her.\r\n\r\nBefore 30 Rock, Mean Girls and 'Sarah Palin', Tina Fey was just a young girl with a dream: a recurring stress dream that she was being chased through a local airport by her middle-school gym teacher.\r\n\r\nShe also had a dream that one day she would be a comedian on TV. She has seen both these dreams come true.\r\n\r\nAt last, Tina Fey's story can be told. From her youthful days as a vicious nerd to her tour of duty on Saturday Night Live; from her passionately halfhearted pursuit of physical beauty to her life as a mother eating things off the floor; from her one-sided college romance to her nearly fatal honeymoon - from the beginning of this paragraph to this final sentence.\r\n\r\nTina Fey reveals all, and proves what we've all suspected: you're no one until someone calls you bossy.",
     'pages': '304 Pages'},
     'images': [],
     'marketprice': '1,095',
     'price': '986',
     'time_scraped': 'Tue Dec  9 13:57:37 2014',
     'title': 'Bossypants',
     'url': 'http://www.libertybooks.com/bookdetail.aspx?pid=16532',
     'vendor': {'order_url': 'http://www.libertybooks.com/bookdetail.aspx?pid=16532',
     'title': 'libertybooks'}} is not JSON serializable
    

我是 scrapy 和 couchdb 的初学者，我也尝试过使用“json.dumps(itm, default=lambda o: o.dict”将项目对象转换为 json 对象, sort_keys=True, indent=4)” 但得到了相同的响应，所以请告诉我有没有办法让我的类 json 可序列化，以便它们可以存储在 couchdb 中？

Answer 1

嗯，更短的答案就是使用 ScrapyJSONEncoder :

from scrapy.utils.serialize import ScrapyJSONEncoder
_encoder = ScrapyJSONEncoder()

    ...

    def saveindb(self,obj):
        logging.debug(obj)
        self.db.save(_encoder.encode(obj))

更长的版本是:如果你想让这个蜘蛛成长(如果它不应该是一次性的)，你可能想要使用 pipeline将项目存储在 CouchDB 中并保持关注点分离(在蜘蛛代码中抓取/抓取，在管道代码中存储在数据库中)。

乍一看这可能看起来像是过度设计，但当项目开始增长并使测试更容易时，它确实有帮助。