Scrapy CrawlSpider用于AJAX内容
AJAX调用的参数是“页面”,每次单击“更多”按钮时都会增加。例如,一次单击“更多”将加载其他n条文章,并在“更多”按钮的onClick事件中更新page参数,以便下次单击“更多”时,将加载两篇文章的“页面”(假设“页面“ 0”最初已加载,而“页面” 1首次点击已加载)。
对于每个“页面”,我想使用“规则”抓取每篇文章的内容,但是我不知道有多少个“页面”,并且我不想选择任意的m(例如10k)。我似乎无法弄清楚如何进行设置。
从这个问题,Scrapy抓取网址才能,我试图创造潜力的URL网址列表,但我不能确定如何以及在何处解析前一个URL,并确保以后从池中发送一个新的URL包含新闻链接为CrawlSpider。我的规则将响应发送到parse_items回调,在该回调中分析文章内容。
在应用规则并调用parse_items之前,是否有办法观察链接页面的内容(类似于BaseSpider示例),这样我才能知道何时停止爬网?
简化的代码(为清楚起见,我删除了一些正在解析的字段):
class ExampleSite(CrawlSpider): name = "so"
download_delay = 2
more_pages = True
current_page = 0
allowed_domains = ['example.com']
start_urls = ['http://example.com/account/ajax_headlines_content?type=in_focus_articles&page=0'+
'&slugs=tsla&is_symbol_page=true']
##could also use
##start_urls = ['http://example.com/symbol/tsla']
ajax_urls = []
for i in range(1,1000):
ajax_urls.append('http://example.com/account/ajax_headlines_content?type=in_focus_articles&page='+str(i)+
'&slugs=tsla&is_symbol_page=true')
rules = (
Rule(SgmlLinkExtractor(allow=('/symbol/tsla', ))),
Rule(SgmlLinkExtractor(allow=('/news-article.*tesla.*', '/article.*tesla.*', )), callback='parse_item')
)
##need something like this??
##override parse?
## if response.body == 'no results':
## self.more_pages = False
## ##stop crawler??
## else:
## self.current_page = self.current_page + 1
## yield Request(self.ajax_urls[self.current_page], callback=self.parse_start_url)
def parse_item(self, response):
self.log("Scraping: %s" % response.url, level=log.INFO)
hxs = Selector(response)
item = NewsItem()
item['url'] = response.url
item['source'] = 'example'
item['title'] = hxs.xpath('//title/text()')
item['date'] = hxs.xpath('//div[@class="article_info_pos"]/span/text()')
yield item
回答:
在这里,spider可能太有限了。如果你需要大量逻辑,通常最好从Spider继承。
Scrapy提供了CloseSpider异常,当你需要在某些情况下停止解析时,可以引发该异常。你正在爬网的页面返回一条消息“你的库存中没有焦点文章”,当你超过最大页面数时,你可以检查此消息并在发生此消息时停止迭代。
在你的情况下,你可以执行以下操作:
from scrapy.spider import Spiderfrom scrapy.http import Request
from scrapy.exceptions import CloseSpider
class ExampleSite(Spider):
name = "so"
download_delay = 0.1
more_pages = True
next_page = 1
start_urls = ['http://example.com/account/ajax_headlines_content?type=in_focus_articles&page=0'+
'&slugs=tsla&is_symbol_page=true']
allowed_domains = ['example.com']
def create_ajax_request(self, page_number):
"""
Helper function to create ajax request for next page.
"""
ajax_template = 'http://example.com/account/ajax_headlines_content?type=in_focus_articles&page={pagenum}&slugs=tsla&is_symbol_page=true'
url = ajax_template.format(pagenum=page_number)
return Request(url, callback=self.parse)
def parse(self, response):
"""
Parsing of each page.
"""
if "There are no Focus articles on your stocks." in response.body:
self.log("About to close spider", log.WARNING)
raise CloseSpider(reason="no more pages to parse")
# there is some content extract links to articles
sel = Selector(response)
links_xpath = "//div[@class='symbol_article']/a/@href"
links = sel.xpath(links_xpath).extract()
for link in links:
url = urljoin(response.url, link)
# follow link to article
# commented out to see how pagination works
#yield Request(url, callback=self.parse_item)
# generate request for next page
self.next_page += 1
yield self.create_ajax_request(self.next_page)
def parse_item(self, response):
"""
Parsing of each article page.
"""
self.log("Scraping: %s" % response.url, level=log.INFO)
hxs = Selector(response)
item = NewsItem()
item['url'] = response.url
item['source'] = 'example'
item['title'] = hxs.xpath('//title/text()')
item['date'] = hxs.xpath('//div[@class="article_info_pos"]/span/text()')
yield item
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