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at September 1, 2012 07:15 by scrapy
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# This middleware can be used to avoid re-visiting already visited items, which can be useful for speeding up the scraping for projects with immutable items, ie. items that, once scraped, don't change. from scrapy import log from scrapy.http import Request from scrapy.item import BaseItem from scrapy.utils.request import request_fingerprint from myproject.items import MyItem class IgnoreVisitedItems(object): """Middleware to ignore re-visiting item pages if they were already visited before. The requests to be filtered by have a meta['filter_visited'] flag enabled and optionally define an id to use for identifying them, which defaults the request fingerprint, although you'd want to use the item id, if you already have it beforehand to make it more robust. """ FILTER_VISITED = 'filter_visited' VISITED_ID = 'visited_id' CONTEXT_KEY = 'visited_ids' def process_spider_output(self, response, result, spider): context = getattr(spider, 'context', {}) visited_ids = context.setdefault(self.CONTEXT_KEY, {}) ret = [] for x in result: visited = False if isinstance(x, Request): if self.FILTER_VISITED in x.meta: visit_id = self._visited_id(x) if visit_id in visited_ids: log.msg("Ignoring already visited: %s" % x.url, level=log.INFO, spider=spider) visited = True elif isinstance(x, BaseItem): visit_id = self._visited_id(response.request) if visit_id: visited_ids[visit_id] = True x['visit_id'] = visit_id x['visit_status'] = 'new' if visited: ret.append(MyItem(visit_id=visit_id, visit_status='old')) else: ret.append(x) return ret def _visited_id(self, request): return request.meta.get(self.VISITED_ID) or request_fingerprint(request) # Snippet imported from snippets.scrapy.org (which no longer works) # author: pablo # date : Aug 10, 2010
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Middleware to avoid re-visiting already visited items
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Python