【问题标题】:How to yield several requests in order in Scrapy?如何在 Scrapy 中按顺序产生多个请求?
【发布时间】:2018-11-16 10:50:21
【问题描述】:

我需要使用 Scrapy按顺序发送我的请求。

def n1(self, response) :
    #self.input = [elem1,elem2,elem3,elem4,elem5, .... ,elem100000]
    for (elem,) in self.input :

        link =  urljoin(path,elem)

        yield Request(link)

我的问题是请求不按顺序排列。 我读了this question,但没有正确答案。

我应该如何更改用于按顺序发送请求的代码?

更新 1

我使用了优先级并将我的代码更改为

def n1(self, response) :

    #self.input = [elem1,elem2,elem3,elem4,elem5, .... ,elem100000]
    self.prio = len(self.input)
    for (elem,) in self.input :
        self.prio -= 1
        link =  urljoin(path,elem)

        yield Request(link, priority=self.prio)

我对这个蜘蛛的设置是

custom_settings = {
    'DOWNLOAD_DELAY' : 0,
    'COOKIES_ENABLED' : True,
    'CONCURRENT_REQUESTS' : 1 ,
    'AUTOTHROTTLE_ENABLED' : False,
}

现在顺序变了,但不是数组中元素的顺序

【问题讨论】:

标签: scrapy python-requests yield


【解决方案1】:

使用return 语句代替yield。

您甚至不需要触摸任何设置:

from scrapy.spiders import Spider, Request

class MySpider(Spider):

    name = 'toscrape.com'
    start_urls = ['http://books.toscrape.com/catalogue/page-1.html']

    urls = (
        'http://books.toscrape.com/catalogue/page-{}.html'.format(i + 1) for i in range(50)
    )

    def parse(self, response):
        for url in self.urls:
            return Request(url)

输出:

2018-11-20 03:35:43 [scrapy.core.engine] DEBUG: Crawled (200) <GET http://books.toscrape.com/catalogue/page-1.html> (referer: http://books.toscrape.com/catalogue/page-1.html)
2018-11-20 03:35:43 [scrapy.core.engine] DEBUG: Crawled (200) <GET http://books.toscrape.com/catalogue/page-2.html> (referer: http://books.toscrape.com/catalogue/page-1.html)
2018-11-20 03:35:44 [scrapy.core.engine] DEBUG: Crawled (200) <GET http://books.toscrape.com/catalogue/page-3.html> (referer: http://books.toscrape.com/catalogue/page-2.html)
2018-11-20 03:35:44 [scrapy.core.engine] DEBUG: Crawled (200) <GET http://books.toscrape.com/catalogue/page-4.html> (referer: http://books.toscrape.com/catalogue/page-3.html)
2018-11-20 03:35:45 [scrapy.core.engine] DEBUG: Crawled (200) <GET http://books.toscrape.com/catalogue/page-5.html> (referer: http://books.toscrape.com/catalogue/page-4.html)
2018-11-20 03:35:45 [scrapy.core.engine] DEBUG: Crawled (200) <GET http://books.toscrape.com/catalogue/page-6.html> (referer: http://books.toscrape.com/catalogue/page-5.html)
2018-11-20 03:35:45 [scrapy.core.engine] DEBUG: Crawled (200) <GET http://books.toscrape.com/catalogue/page-7.html> (referer: http://books.toscrape.com/catalogue/page-6.html)
2018-11-20 03:35:46 [scrapy.core.engine] DEBUG: Crawled (200) <GET http://books.toscrape.com/catalogue/page-8.html> (referer: http://books.toscrape.com/catalogue/page-7.html)
2018-11-20 03:35:46 [scrapy.core.engine] DEBUG: Crawled (200) <GET http://books.toscrape.com/catalogue/page-9.html> (referer: http://books.toscrape.com/catalogue/page-8.html)
2018-11-20 03:35:47 [scrapy.core.engine] DEBUG: Crawled (200) <GET http://books.toscrape.com/catalogue/page-10.html> (referer: http://books.toscrape.com/catalogue/page-9.html)
2018-11-20 03:35:47 [scrapy.core.engine] DEBUG: Crawled (200) <GET http://books.toscrape.com/catalogue/page-11.html> (referer: http://books.toscrape.com/catalogue/page-10.html)
2018-11-20 03:35:47 [scrapy.core.engine] DEBUG: Crawled (200) <GET http://books.toscrape.com/catalogue/page-12.html> (referer: http://books.toscrape.com/catalogue/page-11.html)
2018-11-20 03:35:48 [scrapy.core.engine] DEBUG: Crawled (200) <GET http://books.toscrape.com/catalogue/page-13.html> (referer: http://books.toscrape.com/catalogue/page-12.html)
2018-11-20 03:35:48 [scrapy.core.engine] DEBUG: Crawled (200) <GET http://books.toscrape.com/catalogue/page-14.html> (referer: http://books.toscrape.com/catalogue/page-13.html)
2018-11-20 03:35:49 [scrapy.core.engine] DEBUG: Crawled (200) <GET http://books.toscrape.com/catalogue/page-15.html> (referer: http://books.toscrape.com/catalogue/page-14.html)
2018-11-20 03:35:49 [scrapy.core.engine] DEBUG: Crawled (200) <GET http://books.toscrape.com/catalogue/page-16.html> (referer: http://books.toscrape.com/catalogue/page-15.html)
2018-11-20 03:35:50 [scrapy.core.engine] DEBUG: Crawled (200) <GET http://books.toscrape.com/catalogue/page-17.html> (referer: http://books.toscrape.com/catalogue/page-16.html)
2018-11-20 03:35:50 [scrapy.core.engine] DEBUG: Crawled (200) <GET http://books.toscrape.com/catalogue/page-18.html> (referer: http://books.toscrape.com/catalogue/page-17.html)
2018-11-20 03:35:50 [scrapy.core.engine] DEBUG: Crawled (200) <GET http://books.toscrape.com/catalogue/page-19.html> (referer: http://books.toscrape.com/catalogue/page-18.html)
2018-11-20 03:35:51 [scrapy.core.engine] DEBUG: Crawled (200) <GET http://books.toscrape.com/catalogue/page-20.html> (referer: http://books.toscrape.com/catalogue/page-19.html)
2018-11-20 03:35:51 [scrapy.core.engine] DEBUG: Crawled (200) <GET http://books.toscrape.com/catalogue/page-21.html> (referer: http://books.toscrape.com/catalogue/page-20.html)
2018-11-20 03:35:52 [scrapy.core.engine] DEBUG: Crawled (200) <GET http://books.toscrape.com/catalogue/page-22.html> (referer: http://books.toscrape.com/catalogue/page-21.html)
2018-11-20 03:35:52 [scrapy.core.engine] DEBUG: Crawled (200) <GET http://books.toscrape.com/catalogue/page-23.html> (referer: http://books.toscrape.com/catalogue/page-22.html)
2018-11-20 03:35:53 [scrapy.core.engine] DEBUG: Crawled (200) <GET http://books.toscrape.com/catalogue/page-24.html> (referer: http://books.toscrape.com/catalogue/page-23.html)
2018-11-20 03:35:53 [scrapy.core.engine] DEBUG: Crawled (200) <GET http://books.toscrape.com/catalogue/page-25.html> (referer: http://books.toscrape.com/catalogue/page-24.html)

使用yield 语句,引擎从生成器获取所有响应并以任意顺序执行它们(我怀疑它们可能存储在某种集合中以删除重复项)。

【讨论】:

    【解决方案2】:

    我认为并发请求在这里发挥作用。你可以试试设置

    custom_settings = {
        'CONCURRENT_REQUESTS': 1
    }
    

    默认设置为 8。它可以解释为什么当您有其他工作人员空闲时不会尊重优先级。

    【讨论】:

    • 我有 'CONCURRENT_REQUESTS' : 1 ,'AUTOTHROTTLE_ENABLED' : False,在我的设置中
    【解决方案3】:

    收到上一个请求后才能发送下一个请求:

    class MainSpider(Spider):
        urls = [
            'https://www.url1...',
            'https://www.url2...',
            'https://www.url3...',
        ]
    
        def start_requests(self):
            yield Request(
                url=self.urls[0],
                callback=self.parse,
                meta={'next_index': 1},
            )
    
        def parse(self, response):
            next_index = response.meta['next_index']
    
            # do something with response...
    
            # Process next url
            if next_index < len(self.urls):
                yield Request(
                    url=self.urls[next_index],
                    callback=self.parse,
                    meta={'next_index': next_index+1},
                )
    

    【讨论】:

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