Scrapy(python)TypeError:不可用类型:'list'

Question

我有这个简单的杂乱代码.但是当我使用response.urljoin(port_homepage_url)这部分代码时会出现此错误.

import re

import scrapy
from vesseltracker.items import VesseltrackerItem


class GetVessel(scrapy.Spider):
    name = "getvessel"
    allowed_domains = ["marinetraffic.com"]
    start_urls = [
        'http://www.marinetraffic.com/en/ais/index/ports/all/flag:AE',
    ]

def parse(self, response):
    item = VesseltrackerItem()
    for ports in response.xpath('//table/tr[position()>1]'):
        item['port_name'] = ports.xpath('td[2]/a/text()').extract()
        port_homepage_url = ports.xpath('td[7]/a/@href').extract()
        port_homepage_url = response.urljoin(port_homepage_url)
        yield scrapy.Request(port_homepage_url, callback=self.parse, meta={'item': item})

可能有什么不对？

这是错误日志.

2016-09-30 17:17:13 [scrapy] DEBUG: Crawled (200) <GET http://www.marinetraffic.com/robots.txt> (referer: None)
2016-09-30 17:17:14 [scrapy] DEBUG: Crawled (200) <GET http://www.marinetraffic.com/en/ais/index/ports/all/flag:AE> (referer: None)
2016-09-30 17:17:14 [scrapy] ERROR: Spider error processing <GET http://www.marinetraffic.com/en/ais/index/ports/all/flag:AE> (referer: None)
Traceback (most recent call last):
  File "/Users/noussh/python/env/lib/python2.7/site-packages/scrapy/utils/defer.py", line 102, in iter_errback
    yield next(it)
  File "/Users/noussh/python/env/lib/python2.7/site-packages/scrapy/spidermiddlewares/offsite.py", line 29, in process_spider_output
    for x in result:
  File "/Users/noussh/python/env/lib/python2.7/site-packages/scrapy/spidermiddlewares/referer.py", line 22, in <genexpr>
    return (_set_referer(r) for r in result or ())
  File "/Users/noussh/python/env/lib/python2.7/site-packages/scrapy/spidermiddlewares/urllength.py", line 37, in <genexpr>
    return (r for r in result or () if _filter(r))
  File "/Users/noussh/python/env/lib/python2.7/site-packages/scrapy/spidermiddlewares/depth.py", line 58, in <genexpr>
    return (r for r in result or () if _filter(r))
  File "/Users/noussh/python/vesseltracker/vesseltracker/spiders/marinetraffic.py", line 19, in parse
    port_homepage_url = response.urljoin(port_homepage_url)
  File "/Users/noussh/python/env/lib/python2.7/site-packages/scrapy/http/response/text.py", line 78, in urljoin
    return urljoin(get_base_url(self), url)
  File "/usr/local/Cellar/python/2.7.12/Frameworks/Python.framework/Versions/2.7/lib/python2.7/urlparse.py", line 261, in urljoin
    urlparse(url, bscheme, allow_fragments)
  File "/usr/local/Cellar/python/2.7.12/Frameworks/Python.framework/Versions/2.7/lib/python2.7/urlparse.py", line 143, in urlparse
    tuple = urlsplit(url, scheme, allow_fragments)
  File "/usr/local/Cellar/python/2.7.12/Frameworks/Python.framework/Versions/2.7/lib/python2.7/urlparse.py", line 176, in urlsplit
    cached = _parse_cache.get(key, None)
TypeError: unhashable type: 'list'

Answer 1

返回ports.xpath('td[7]/a/@href').extract()一个列表，当您尝试对其执行“urljoin”时，它会失败。改用extract_first()：

port_homepage_url = ports.xpath('td[7]/a/@href').extract_first()