当我执行下面的代码时，我能够只提取一个链接，而不是提取该网站特定页面的所有链接。
from scrapy import Spider
from scrapy.http import Request
class BooksSpider(Spider):
name = 'books'
allowed_domains = ['books.toscrape.com/']
start_urls= ["http://books.toscrape.com"]
def parse(self, response):
books = response.xpath("//h3/a/@href").extract()
for book in books:
absolute_url = response.urljoin(book)
yield Request(absolute_url), callback=self.parse_page)
def parse_page(self, response):
pass
这是输出的结果，它只提取了网站 "books.toscrape.com "的第一个链接。谁能帮我了解一下这里的错误是什么，还是因为系统错误。现在太令人沮丧了，因为所有的循环和其他的东西都很好。我猜YIELD有一些问题，我怎么能处理这个错误呢？
2020-05-26 12:09:23 [scrapy.utils.log] INFO: Scrapy 2.1.0 started (bot: scrap_book)
2020-05-26 12:09:23 [scrapy.utils.log] INFO: Versions: lxml 4.5.1.0, libxml2 2.9.5, cssselect 1.1.0, parsel 1.6.0, w3lib 1.22.0, Twisted 20.3.0, Python 3.8.2 (tags/v3.8.2:7b3ab59, Feb 25 2020, 22:45:29) [MSC v.1916 32 bit (Intel)], pyOpenSSL 19.1.0 (OpenSSL 1.1.1g 21 Apr 2020), cryptography 2.9.2, Platform Windows-10-10.0.18362-SP0
2020-05-26 12:09:23 [scrapy.utils.log] DEBUG: Using reactor: twisted.internet.selectreactor.SelectReactor
2020-05-26 12:09:23 [scrapy.crawler] INFO: Overridden settings:
{'BOT_NAME': 'scrap_book',
'NEWSPIDER_MODULE': 'scrap_book.spiders',
'ROBOTSTXT_OBEY': True,
'SPIDER_MODULES': ['scrap_book.spiders']}
2020-05-26 12:09:23 [scrapy.extensions.telnet] INFO: Telnet Password: 7b1edefe67af4658
2020-05-26 12:09:23 [scrapy.middleware] INFO: Enabled extensions:
['scrapy.extensions.corestats.CoreStats',
'scrapy.extensions.telnet.TelnetConsole',
'scrapy.extensions.logstats.LogStats']
2020-05-26 12:09:25 [scrapy.middleware] INFO: Enabled downloader middlewares:
['scrapy.downloadermiddlewares.robotstxt.RobotsTxtMiddleware',
'scrapy.downloadermiddlewares.httpauth.HttpAuthMiddleware',
'scrapy.downloadermiddlewares.downloadtimeout.DownloadTimeoutMiddleware',
'scrapy.downloadermiddlewares.defaultheaders.DefaultHeadersMiddleware',
'scrapy.downloadermiddlewares.useragent.UserAgentMiddleware',
'scrapy.downloadermiddlewares.retry.RetryMiddleware',
'scrapy.downloadermiddlewares.redirect.MetaRefreshMiddleware',
'scrapy.downloadermiddlewares.httpcompression.HttpCompressionMiddleware',
'scrapy.downloadermiddlewares.redirect.RedirectMiddleware',
'scrapy.downloadermiddlewares.cookies.CookiesMiddleware',
'scrapy.downloadermiddlewares.httpproxy.HttpProxyMiddleware',
'scrapy.downloadermiddlewares.stats.DownloaderStats']
2020-05-26 12:09:25 [scrapy.middleware] INFO: Enabled spider middlewares:
['scrapy.spidermiddlewares.httperror.HttpErrorMiddleware',
'scrapy.spidermiddlewares.offsite.OffsiteMiddleware',
'scrapy.spidermiddlewares.referer.RefererMiddleware',
'scrapy.spidermiddlewares.urllength.UrlLengthMiddleware',
'scrapy.spidermiddlewares.depth.DepthMiddleware']
2020-05-26 12:09:26 [scrapy.middleware] INFO: Enabled item pipelines:
[]
2020-05-26 12:09:26 [scrapy.core.engine] INFO: Spider opened
2020-05-26 12:09:26 [scrapy.extensions.logstats] INFO: Crawled 0 pages (at 0 pages/min), scraped 0 items (at 0 items/min)
2020-05-26 12:09:26 [scrapy.extensions.telnet] INFO: Telnet console listening on 127.0.0.1:6024
2020-05-26 12:09:26 [scrapy.core.engine] DEBUG: Crawled (404) <GET http://books.toscrape.com/robots.txt> (referer: None)
2020-05-26 12:09:26 [scrapy.core.engine] DEBUG: Crawled (200) <GET http://books.toscrape.com> (referer: None)
2020-05-26 12:09:27 [scrapy.spidermiddlewares.offsite] DEBUG: Filtered offsite request to 'books.toscrape.com': <GET http://books.toscrape.com/catalogue/a-light-in-the-attic_1000/ind 'response_received_count': 2,
'robotstxt/request_count': 1,
'robotstxt/response_count': 1,
'robotstxt/response_status_count/404': 1,
'scheduler/dequeued': 1,
'scheduler/dequeued/memory': 1,
'scheduler/enqueued': 1,
'scheduler/enqueued/memory': 1,
'start_time': datetime.datetime(2020, 5, 26, 6, 24, 26, 117907)}
2020-05-26 12:09:28 [scrapy.core.engine] INFO: Spider closed (finished)
就像Scrapy说的那样，链接会因为你的allow_domains而被过滤。DEBUG: Filtered offsite request to 'books.toscrape.com'
把你的代码改成 allowed_domains = ['books.toscrape.com'] 就可以正常工作了。
另外，在你发的代码中，由于后面的括号太多了，所以在收益率中出现了错误。absolute_url. 应该是这样的 yield Request(absolute_url, callback=self.parse_page)