图片路径存储且item的json化

1.item_completed()方法

• 语法：item_completed(results, items, info)；

• 当一个单独项目中的全部图片请求完成时（无论下载成功或者失败），ImagesPipeline.item_completed() 方法将被调用。item_completed()方法必须返回将发送到后续item pipeline阶段的输出，所以必须返回或删除item（默认状况下item_completed会返回所有item）；

2.在pipline中重写item_completed方法

• 在ImagePipeline中重写item_completed方法获取图片的保存路径

class ImagePipeline(ImagesPipeline):
    def file_path(self, request, response=None, info=None):
        ## start of deprecation warning block (can be removed in the future)
        def _warn():
            from scrapy.exceptions import ScrapyDeprecationWarning
            import warnings
            warnings.warn('ImagesPipeline.image_key(url) and file_key(url) methods are deprecated, '
                          'please use file_path(request, response=None, info=None) instead',
                          category=ScrapyDeprecationWarning, stacklevel=1)
        # check if called from image_key or file_key with url as first argument
        if not isinstance(request, Request):
            _warn()
            url = request
        else:
            url = request.url
        # detect if file_key() or image_key() methods have been overridden
        if not hasattr(self.file_key, '_base'):
            _warn()
            return self.file_key(url)
        elif not hasattr(self.image_key, '_base'):
            _warn()
            return self.image_key(url)
        ## end of deprecation warning block
        image_guid = hashlib.sha1(to_bytes(url)).hexdigest()  # change to request.url after deprecation
        # 修改成时间为目录
        return '{}/{}.jpg'.format(datetime.now().year,image_guid)
    def item_completed(self, results, item, info):
        # 获取图片地址保存到列表中
        values = [value['path'] for ok, value in results if ok]
        # 给item赋值
        item['image_path'] = values.pop(0) if values else 'default.jpg'
        return item

3.建立md5函数

• 咱们能够使用scrapy中的hashlib.md5 处理 url，首先在项目settings文件的同一目录下，建立一个叫utils的package，而后在这个包里建立一个md5文件； 使用以前先从hashlib中导入md5，把hashlib中md5()实例化，而后用update传入url，再用 hexdigest() 提取摘要。还能够使用isinstance()来判判断传入值编码类型，使用encode()方法将unicode编码转换成其余编码的字符串等；

from hashlib import md5
def get_md5(url):
    if isinstance(url, str):
        # 先转化为字节码
        url = url.encode()
        print(url)
    obj = md5()
    obj.update(url)
    return obj.hexdigest()
if __name__ == '__main__':
    print(get_md5('www.baidu.com'))

4. 在item中添加字段

import scrapy
class XkdDribbbleSpiderItem(scrapy.Item):
    title = scrapy.Field()
    image_url = scrapy.Field()
    date = scrapy.Field()
    # 添加图片路径到item中
    image_path = scrapy.Field()
    # 加页面的url地址添加到item中
    url = scrapy.Field()
    # 添加url的哈希值字段
    url_id = scrapy.Field()

5. 将item在spider中返回

import scrapy
from urllib import parse
from scrapy.http import Request
from datetime import datetime
from ..items import XkdDribbbleSpiderItem
from ..utils.md5_tool import get_md5
class DribbbleSpider(scrapy.Spider):
    name = 'dribbble'
    allowed_domains = ['dribbble.com']
    start_urls = ['https://dribbble.com/stories']
    def parse(self, response):
        # 获取a标签的url值
        # selector
        a_selectors = response.css('div.teaser a')
        for a_selector in a_selectors:
            image_url = a_selector.css('img::attr(src)').extract()[0]
            page_url = a_selector.css('::attr(href)').extract()[0]
            yield Request(url=parse.urljoin(response.url, page_url), callback=self.parse_analyse,meta={'a_image_url': image_url})
    def parse_analyse(self, response):
        title = response.css('header h1::text').extract_first()
        image_url = response.meta.get('a_image_url')
        date_raw = response.css('p span.date::text').extract()[0]
        date_str = date_raw.strip()
        date = datetime.strptime(date_str, '%b %d, %Y').date()
        item = XkdDribbbleSpiderItem()
        item['title'] = title
        item['image_url'] = [image_url]
        item['date'] = date
        item['url'] = response.url
        item['url_id'] = get_md5(response.url)
        # item数据模型进行落地，数据持久化
        yield item

6.建立JsonSavePipeline，用于写入item到文件中

import codecs
import json

class JsonSavePipeline:
    def process_item(self, item, spider):
        # 将spider中返回的item转化为字典
        file = codecs.open('blog.json', mode='a')
        dict_item = dict(item)
        # 将字典json化
        line = json.dumps(dict_item, ensure_ascii=False) + '\n'
        # 写入到文件
        file.write(line)
        # 再次返回item
        file.close()

7.在settings文件中添加JsonSavePipeline

'XKD_Dribbble_Spider.pipelines.JsonSavePipeline': 2,

参考：https://www.9xkd.com/user/plan-view.html?id=1871857091