python - 为特定的scrapy请求添加延迟

Question

是否可以延迟特定scrapy请求的重试。我有一个中间件，它需要将页面请求推迟到稍后的时间。我知道如何进行基本的延迟(队列结束)，以及如何延迟所有请求(全局设置)，但我只想延迟这个单独的请求。这在队列末尾附近最重要，如果我进行简单的延迟，它会立即再次成为下一个请求。

Answer 1

方法一
一种方法是为您的 Spider 添加一个中间件( source ， linked ):

# File: middlewares.py

from twisted.internet import reactor
from twisted.internet.defer import Deferred


class DelayedRequestsMiddleware(object):
    def process_request(self, request, spider):
        delay_s = request.meta.get('delay_request_by', None)
        if not delay_s:
            return

        deferred = Deferred()
        reactor.callLater(delay_s, deferred.callback, None)
        return deferred

你以后可以像这样在你的蜘蛛中使用它:

import scrapy


class QuotesSpider(scrapy.Spider):
    name = "quotes"
    custom_settings = {
        'DOWNLOADER_MIDDLEWARES': {'middlewares.DelayedRequestsMiddleware': 123},
    }

    def start_requests(self):
        # This request will have itself delayed by 5 seconds
        yield scrapy.Request(url='http://quotes.toscrape.com/page/1/', 
                             meta={'delay_request_by': 5})
        # This request will not be delayed
        yield scrapy.Request(url='http://quotes.toscrape.com/page/2/')

    def parse(self, response):
        ...  # Process results here

方法二
您可以使用自定义重试中间件 ( source ) 执行此操作，您只需要覆盖 process_response当前的方法 Retry Middleware :

from scrapy.downloadermiddlewares.retry import RetryMiddleware
from scrapy.utils.response import response_status_message


class CustomRetryMiddleware(RetryMiddleware):

    def process_response(self, request, response, spider):
        if request.meta.get('dont_retry', False):
            return response
        if response.status in self.retry_http_codes:
            reason = response_status_message(response.status)

            # Your delay code here, for example sleep(10) or polling server until it is alive

            return self._retry(request, reason, spider) or response

        return response

然后启用它而不是默认的 RetryMiddleware在 settings.py :

DOWNLOADER_MIDDLEWARES = {
    'scrapy.downloadermiddlewares.retry.RetryMiddleware': None,
    'myproject.middlewarefilepath.CustomRetryMiddleware': 550,
}