Scrapy 头痛 - 尝试调试。没有错误，但代码不起作用

Question

编辑:这个问题已经解决了! XPATH 是问题所在。

我很困惑。我正在尝试编写一个非常简单的蜘蛛，抓取一个网站(talkbass.com)以获得分类低音部分中所有链接的列表(http://www.talkbass.com/forum/f126/) 。我根据教程编写了蜘蛛程序(我相对轻松地完成了该教程)，但这个程序不起作用。我可能做错了很多，因为我也尝试纳入一条规则，但我什么也没得到。

我的商品代码是:

from scrapy.item import Item, Field
class BassItem(Item):
    title = Field()
    link = Field()
    print title, link

我的蜘蛛代码是:

from scrapy.spider import BaseSpider 
from scrapy.contrib.spiders import Rule 
from scrapy.contrib.linkextractors.sgml import SgmlLinkExtractor 
from scrapy.selector import HtmlXPathSelector
from tutorial.items import BassItem
class BassSpider(BaseSpider):
    name = "bass"
    allowed_domains = ["www.talkbass.com"]
    start_urls = ["http://www.talkbass.com/forum/f126/"]

    rules = (
        # Extract links matching 'f126/xxx'
        # and follow links from them (since no callback means follow=True by default).
        Rule(SgmlLinkExtractor(allow=('/f126/(\d*)/', ), ))
    )

    def parse(self, response):
        hxs = HtmlXPathSelector(response)
        ads = hxs.select('/html/body/div/div/div/table/tbody/tr/td/form/table/tbody')
        items = []
        for ad in ads:
            item = BassItem()
            item['title'] = ad.select('a/text()').extract()
            item['link'] = ad.select('a/@href').extract()
            items.append(item)
        return items

我没有收到任何错误，但日志没有返回任何内容。这是我在控制台中看到的内容:

C:\Python27\Scrapy\tutorial>scrapy crawl bass
2013-01-07 14:36:49+0800 [scrapy] INFO: Scrapy 0.16.3 started (bot: tutorial)
2013-01-07 14:36:49+0800 [scrapy] DEBUG: Enabled extensions: LogStats, TelnetConsole, CloseSpider, WebService, Co
reStats, SpiderState
{} {}
2013-01-07 14:36:51+0800 [scrapy] DEBUG: Enabled downloader middlewares: HttpAuthMiddleware, DownloadTimeoutMiddl
eware, UserAgentMiddleware, RetryMiddleware, DefaultHeadersMiddleware, RedirectMiddleware, CookiesMiddleware, Htt
pCompressionMiddleware, ChunkedTransferMiddleware, DownloaderStats
2013-01-07 14:36:51+0800 [scrapy] DEBUG: Enabled spider middlewares: HttpErrorMiddleware, OffsiteMiddleware, Refe
rerMiddleware, UrlLengthMiddleware, DepthMiddleware
2013-01-07 14:36:51+0800 [scrapy] DEBUG: Enabled item pipelines:
2013-01-07 14:36:51+0800 [bass] INFO: Spider opened
2013-01-07 14:36:51+0800 [bass] INFO: Crawled 0 pages (at 0 pages/min), scraped 0 items (at 0 items/min)
2013-01-07 14:36:51+0800 [scrapy] DEBUG: Telnet console listening on 0.0.0.0:6023
2013-01-07 14:36:51+0800 [scrapy] DEBUG: Web service listening on 0.0.0.0:6080
2013-01-07 14:36:52+0800 [bass] DEBUG: Crawled (200) <GET http://www.talkbass.com/forum/f126/> (referer: None)
2013-01-07 14:36:52+0800 [bass] INFO: Closing spider (finished)
2013-01-07 14:36:52+0800 [bass] INFO: Dumping Scrapy stats:
        {'downloader/request_bytes': 233,
         'downloader/request_count': 1,
         'downloader/request_method_count/GET': 1,
         'downloader/response_bytes': 17997,
         'downloader/response_count': 1,
         'downloader/response_status_count/200': 1,
         'finish_reason': 'finished',
         'finish_time': datetime.datetime(2013, 1, 7, 6, 36, 52, 305000),
         'log_count/DEBUG': 7,
         'log_count/INFO': 4,
         'response_received_count': 1,
         'scheduler/dequeued': 1,
         'scheduler/dequeued/memory': 1,
         'scheduler/enqueued': 1,
         'scheduler/enqueued/memory': 1,
         'start_time': datetime.datetime(2013, 1, 7, 6, 36, 51, 458000)}
2013-01-07 14:36:52+0800 [bass] INFO: Spider closed (finished)

我从未做过实际的项目，我认为这将是一个很好的起点，但我似乎无法解决这个问题。

我也不确定 XPath 是否正确。我正在使用名为 XPath helper 的 Chrome 扩展。我需要的部分之一的示例如下:

/html/body/div[1]/div[@class='page']/div/table[5]/tbody/tr/td[2]/form[@id='inlinemodform']/table[@id='threadslist']/tbody[@id='threadbitsforum126']/tr[6]/td[@id='td_threadtitle944468']/div[1]/a[@id='thread_title944468']

但是，如果您看到“tr[6] ”和“944468” - 这些对于每个链接来说都不是恒定的(其他一切都是)。我刚刚删除了类名称和数字，留下了您在蜘蛛代码中看到的内容。

另外只是添加 - 当我直接从 XPath Helper 复制并粘贴 XPath 时，它会给出语法错误:

    ads = hxs.select('/html/body/div[1]/div[@class='page']/div/table[5]/tbody/tr/td[2]/form[@id='inlinemodform']/table[@id='threadslist']/tbody[@id='threadbits_forum_126']/tr[6]/td[@id='td_threadtitle_944468']/div[1]/a[@id='thread_title_944468']')
                                                                                                                                                                                       ^
SyntaxError: invalid syntax

我尝试过解决这个问题(在元素不恒定的情况下使用通配符)，并且每次尝试时都会收到语法错误

Answer 1

可能导致该问题的一个原因是您使用的 BaseSpider 未实现规则。

尝试将 BaseSpider 更改为 CrawlSpider。您还应该将 parse 重命名为 parse_item (因为 CrawlSpider 实现了 parse 函数)，这将需要在您的规则中显式设置回调。例如:

rules = (
    # Extract links matching 'f126/xxx'
    # and follow links from them (since no callback means follow=True by default).
    Rule(SgmlLinkExtractor(allow=('index\d+\.html', )), callback='parse_item'),
)

要尝试的更新的 Xpath 如下。请注意，这将包括所有粘性线程，因此将其作为练习留给 OP 来找出如何过滤掉这些线程。

ads = hxs.select("//td[substring(@id, 1, 15) = 'td_threadtitle_']/div/a")