为什么XMLFeedSpider无法遍历指定的节点？

时间：2015-02-05 23:23:05

标签： python xml rss scrapy scrapy-spider

我试图解析PLoS的RSS源以获取新的出版物。 RSS源位于here。

下面是我的蜘蛛：

from scrapy.contrib.spiders import XMLFeedSpider


class PLoSSpider(XMLFeedSpider):
    name = "plos"
    itertag = 'entry'
    allowed_domains = ["plosone.org"]
    start_urls = [
         ('http://www.plosone.org/article/feed/search'
          '?unformattedQuery=*%3A*&sort=Date%2C+newest+first')
    ]

    def parse_node(self, response, node):
        pass

此配置生成以下日志输出（请注意例外）：

$ scrapy crawl plos
2015-02-06 00:19:08+0100 [scrapy] INFO: Scrapy 0.24.4 started (bot: plos)
2015-02-06 00:19:08+0100 [scrapy] INFO: Optional features available: ssl, http11, boto
2015-02-06 00:19:08+0100 [scrapy] INFO: Overridden settings: {'NEWSPIDER_MODULE': 'plos.spiders', 'SPIDER_MODULES': ['plos.spiders'], 'BOT_NAME': 'plos'}
2015-02-06 00:19:08+0100 [scrapy] INFO: Enabled extensions: LogStats, TelnetConsole, CloseSpider, WebService, CoreStats, SpiderState
2015-02-06 00:19:08+0100 [scrapy] INFO: Enabled downloader middlewares: HttpAuthMiddleware, DownloadTimeoutMiddleware, UserAgentMiddleware, RetryMiddleware, DefaultHeadersMiddleware, MetaRefreshMiddleware, HttpCompressionMiddleware, RedirectMiddleware, CookiesMiddleware, ChunkedTransferMiddleware, DownloaderStats
2015-02-06 00:19:08+0100 [scrapy] INFO: Enabled spider middlewares: HttpErrorMiddleware, OffsiteMiddleware, RefererMiddleware, UrlLengthMiddleware, DepthMiddleware
2015-02-06 00:19:08+0100 [scrapy] INFO: Enabled item pipelines: 
2015-02-06 00:19:08+0100 [plos] INFO: Spider opened
2015-02-06 00:19:08+0100 [plos] INFO: Crawled 0 pages (at 0 pages/min), scraped 0 items (at 0 items/min)
2015-02-06 00:19:08+0100 [scrapy] DEBUG: Telnet console listening on 127.0.0.1:6023
2015-02-06 00:19:08+0100 [scrapy] DEBUG: Web service listening on 127.0.0.1:6080
2015-02-06 00:19:09+0100 [plos] DEBUG: Crawled (200) <GET http://www.plosone.org/article/feed/search?unformattedQuery=*%3A*&sort=Date%2C+newest+first> (referer: None)
2015-02-06 00:19:09+0100 [plos] ERROR: Spider error processing <GET http://www.plosone.org/article/feed/search?unformattedQuery=*%3A*&sort=Date%2C+newest+first>
    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/feed.py", line 61, in parse_nodes
        for selector in nodes:
      File "/usr/local/lib/python2.7/dist-packages/scrapy/contrib/spiders/feed.py", line 87, in _iternodes
        for node in xmliter(response, self.itertag):
      File "/usr/local/lib/python2.7/dist-packages/scrapy/utils/iterators.py", line 31, in xmliter
        yield Selector(text=nodetext, type='xml').xpath('//' + nodename)[0]
    exceptions.IndexError: list index out of range

2015-02-06 00:19:09+0100 [plos] INFO: Closing spider (finished)
2015-02-06 00:19:09+0100 [plos] INFO: Dumping Scrapy stats:
    {'downloader/request_bytes': 282,
     'downloader/request_count': 1,
     'downloader/request_method_count/GET': 1,
     'downloader/response_bytes': 7590,
     'downloader/response_count': 1,
     'downloader/response_status_count/200': 1,
     'finish_reason': 'finished',
     'finish_time': datetime.datetime(2015, 2, 5, 23, 19, 9, 379574),
     'log_count/DEBUG': 3,
     'log_count/ERROR': 1,
     'log_count/INFO': 7,
     'response_received_count': 1,
     'scheduler/dequeued': 1,
     'scheduler/dequeued/memory': 1,
     'scheduler/enqueued': 1,
     'scheduler/enqueued/memory': 1,
     'spider_exceptions/IndexError': 1,
     'start_time': datetime.datetime(2015, 2, 5, 23, 19, 8, 834428)}
2015-02-06 00:19:09+0100 [plos] INFO: Spider closed (finished)

将itertag = "entry"更改为itertag = "//entry"会删除该异常，但不会删除任何项目。我还尝试使用scrapy.log.msg来记录parse_node内的消息，但没有出现任何内容，也没有报告任何节点已被删除。

我做错了什么？

修改

根据alecxe的建议，这里是一个定义了名称空间的蜘蛛。文档有点吝啬，所以我还不确定为什么我的日志调用没有出现...... 

from scrapy import log
from scrapy.contrib.spiders import XMLFeedSpider


class PLoSSpider(XMLFeedSpider):
    name = "plos"
    allowed_domains = ["plosone.org"]
    namespaces = [
        (
            'plos',
            ('http://www.plosone.org/article/feed/search'
             '?unformattedQuery=*%3A*&sort=Date%2C+newest+first')
        )
    ]
    itertag = 'plos:entry'

def parse_node(self, response, node):
    log.msg('*** PING ***')

这是输出：

$ scrapy crawl plos
2015-02-06 18:33:01+0100 [scrapy] INFO: Scrapy 0.24.4 started (bot: plos)
2015-02-06 18:33:01+0100 [scrapy] INFO: Optional features available: ssl, http11, boto
2015-02-06 18:33:01+0100 [scrapy] INFO: Overridden settings: {'NEWSPIDER_MODULE': 'plos.spiders', 'SPIDER_MODULES': ['plos.spiders'], 'BOT_NAME': 'plos'}
2015-02-06 18:33:01+0100 [scrapy] INFO: Enabled extensions: LogStats, TelnetConsole, CloseSpider, WebService, CoreStats, SpiderState
2015-02-06 18:33:02+0100 [scrapy] INFO: Enabled downloader middlewares: HttpAuthMiddleware, DownloadTimeoutMiddleware, UserAgentMiddleware, RetryMiddleware, DefaultHeadersMiddleware, MetaRefreshMiddleware, HttpCompressionMiddleware, RedirectMiddleware, CookiesMiddleware, ChunkedTransferMiddleware, DownloaderStats
2015-02-06 18:33:02+0100 [scrapy] INFO: Enabled spider middlewares: HttpErrorMiddleware, OffsiteMiddleware, RefererMiddleware, UrlLengthMiddleware, DepthMiddleware
2015-02-06 18:33:02+0100 [scrapy] INFO: Enabled item pipelines: 
2015-02-06 18:33:02+0100 [plos] INFO: Spider opened
2015-02-06 18:33:02+0100 [plos] INFO: Crawled 0 pages (at 0 pages/min), scraped 0 items (at 0 items/min)
2015-02-06 18:33:02+0100 [scrapy] DEBUG: Telnet console listening on 127.0.0.1:6023
2015-02-06 18:33:02+0100 [scrapy] DEBUG: Web service listening on 127.0.0.1:6080
2015-02-06 18:33:02+0100 [plos] INFO: Closing spider (finished)
2015-02-06 18:33:02+0100 [plos] INFO: Dumping Scrapy stats:
    {'finish_reason': 'finished',
     'finish_time': datetime.datetime(2015, 2, 6, 17, 33, 2, 65414),
     'log_count/DEBUG': 2,
     'log_count/INFO': 7,
     'start_time': datetime.datetime(2015, 2, 6, 17, 33, 2, 60311)}
2015-02-06 18:33:02+0100 [plos] INFO: Spider closed (finished)

应进一步注意，运行scrapy shell "http://www.plosone.org/article/feed/search?unformattedQuery=*%3A*&sort=Date%2C+newest+first"后跟response.xpath('//entry')会产生一个空列表（[]）。但是，如果查看原始XML数据，您可以看到<entry>标记为白天。我完全失去了，在这里......

1 个答案:

答案 0 :(得分：2)

您需要处理namespaces ：

class PLoSSpider(XMLFeedSpider):
    name = "plos"

    namespaces = [('atom', 'http://www.w3.org/2005/Atom')]
    itertag = 'atom:entry'
    iterator = 'xml'  # this is also important

另见：

工作示例：

from scrapy.contrib.spiders import XMLFeedSpider


class PLoSSpider(XMLFeedSpider):
    name = "plos"

    namespaces = [('atom', 'http://www.w3.org/2005/Atom')]
    itertag = 'atom:entry'
    iterator = 'xml'

    allowed_domains = ["plosone.org"]
    start_urls = [
         ('http://www.plosone.org/article/feed/search'
          '?unformattedQuery=*%3A*&sort=Date%2C+newest+first')
    ]

    def parse_node(self, response, node):
        print node
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