Biegral Blog

###一、scrapy图片爬虫构建思路
1.分析网站
2.选择爬取方式与策略
3.创建爬虫项目 → 定义items.py
4.编写爬虫文件
5.编写pipelines与setting
6.调试

二、千图网难点（http://www.58pic.com/）

1.要爬取全站的图片
2.要爬取高清的图片------找出高清地址即可
3.要有相应的反爬虫机制------如模拟浏览器，不记录cookie等，只要相应注释去掉即可COOKIES_ENABLED = False

三、散点知识

1.from scrapy.http import Request 是回调函数用Request(url=…,callback=…)
2.xpath的//表示提取所有符合的节点

代码：

items.py

import scrapy
class QiantuwangItem(scrapy.Item):
    # define the fields for your item here like:
    # name = scrapy.Field()
    url = scrapy.Field()
    title = scrapy.Field()

middlewares.py

from scrapy import signals


class QiantuwangSpiderMiddleware(object):
    # Not all methods need to be defined. If a method is not defined,
    # scrapy acts as if the spider middleware does not modify the
    # passed objects.

    @classmethod
    def from_crawler(cls, crawler):
        # This method is used by Scrapy to create your spiders.
        s = cls()
        crawler.signals.connect(s.spider_opened, signal=signals.spider_opened)
        return s

    def process_spider_input(response, spider):
        # Called for each response that goes through the spider
        # middleware and into the spider.

        # Should return None or raise an exception.
        return None

    def process_spider_output(response, result, spider):
        # Called with the results returned from the Spider, after
        # it has processed the response.

        # Must return an iterable of Request, dict or Item objects.
        for i in result:
            yield i

    def process_spider_exception(response, exception, spider):
        # Called when a spider or process_spider_input() method
        # (from other spider middleware) raises an exception.

        # Should return either None or an iterable of Response, dict
        # or Item objects.
        pass

    def process_start_requests(start_requests, spider):
        # Called with the start requests of the spider, and works
        # similarly to the process_spider_output() method, except
        # that it doesn’t have a response associated.

        # Must return only requests (not items).
        for r in start_requests:
            yield r

    def spider_opened(self, spider):
        spider.logger.info('Spider opened: %s' % spider.name)

import urllib
import random
class QiantuwangPipeline(object):
    def process_item(self, item, spider):
        try:
            title = item['title'][0].encode('gbk')
            file = "E:/tupian/" + str(title) + str(int(random.random() * 10000)) + ".jpg"
            urllib.urlretrieve(item['url'][0], filename=file)
        except Exception, e:
            print e
            pass
        return item