[英]Scrapy start_urls
from scrapy.spider import Spider
from scrapy.selector import Selector
from dirbot.items import Website
class DmozSpider(Spider):
name = "dmoz"
allowed_domains = ["dmoz.org"]
start_urls = [
"http://www.dmoz.org/Computers/Programming/Languages/Python/Books/",
"http://www.dmoz.org/Computers/Programming/Languages/Python/Resources/",
]
def parse(self, response):
"""
The lines below is a spider contract. For more info see:
http://doc.scrapy.org/en/latest/topics/contracts.html
@url http://www.dmoz.org/Computers/Programming/Languages/Python/Resources/
@scrapes name
"""
sel = Selector(response)
sites = sel.xpath('//ul[@class="directory-url"]/li')
items = []
for site in sites:
item = Website()
item['name'] = site.xpath('a/text()').extract()
item['url'] = site.xpath('a/@href').extract()
item['description'] = site.xpath('text()').re('-\s[^\n]*\\r')
items.append(item)
return items
但为什么它只刮掉这两个网页? 我看到allowed_domains = ["dmoz.org"]
但是这两个页面还包含指向dmoz.org
域内其他页面的链接! 为什么它也不刮它们?
start_urls
类属性包含start urls - 仅此而已。 如果你已经提取了你要抓取的其他页面的网址 - 通过[另一个]回调来parse
回调相应的请求:
class Spider(BaseSpider):
name = 'my_spider'
start_urls = [
'http://www.domain.com/'
]
allowed_domains = ['domain.com']
def parse(self, response):
'''Parse main page and extract categories links.'''
hxs = HtmlXPathSelector(response)
urls = hxs.select("//*[@id='tSubmenuContent']/a[position()>1]/@href").extract()
for url in urls:
url = urlparse.urljoin(response.url, url)
self.log('Found category url: %s' % url)
yield Request(url, callback = self.parseCategory)
def parseCategory(self, response):
'''Parse category page and extract links of the items.'''
hxs = HtmlXPathSelector(response)
links = hxs.select("//*[@id='_list']//td[@class='tListDesc']/a/@href").extract()
for link in links:
itemLink = urlparse.urljoin(response.url, link)
self.log('Found item link: %s' % itemLink, log.DEBUG)
yield Request(itemLink, callback = self.parseItem)
def parseItem(self, response):
...
如果您仍想自定义创建启动请求,请覆盖方法BaseSpider.start_requests()
start_urls包含蜘蛛开始爬行的链接。 如果要递归爬网,则应使用crawlspider并为其定义规则。 http://doc.scrapy.org/en/latest/topics/spiders.html以此为例。
该类没有rules
属性。 查看http://readthedocs.org/docs/scrapy/en/latest/intro/overview.html并搜索“规则”以查找示例。
如果您在回调中使用BaseSpider
,则必须自己提取所需的URL并返回Request
对象。
如果您使用CrawlSpider
,则链接提取将由规则和与规则关联的SgmlLinkExtractor处理。
如果您使用规则来跟踪链接(已经在scrapy中实现),蜘蛛也会刮掉它们。 我希望有帮助......
from scrapy.contrib.spiders import BaseSpider, Rule
from scrapy.contrib.linkextractors.sgml import SgmlLinkExtractor
from scrapy.selector import HtmlXPathSelector
class Spider(BaseSpider):
name = 'my_spider'
start_urls = ['http://www.domain.com/']
allowed_domains = ['domain.com']
rules = [Rule(SgmlLinkExtractor(allow=[], deny[]), follow=True)]
...
你没有编写函数来处理url你想要得到的东西。还有两种方法来解析。使用规则(crawlspider)2:编写处理新urls的函数。并将它们放在回调函数中。
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