圖片路徑存儲且item的json化

1.item_completed()方法

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

• 當一個單獨項目中的全部圖片請求完成時（無論下載成功或者失敗），ImagesPipeline.item_completed() 方法將被調用。item_completed()方法必須返回將發送到後續item pipeline階段的輸出，所以必須返回或刪除item（默認狀況下item_completed會返回所有item）；

2.在pipline中重寫item_completed方法

• 在ImagePipeline中重寫item_completed方法獲取圖片的保存路徑

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
        # 修改成時間爲目錄
        return '{}/{}.jpg'.format(datetime.now().year,image_guid)
    def item_completed(self, results, item, info):
        # 獲取圖片地址保存到列表中
        values = [value['path'] for ok, value in results if ok]
        # 給item賦值
        item['image_path'] = values.pop(0) if values else 'default.jpg'
        return item

3.建立md5函數

• 咱們能夠使用scrapy中的hashlib.md5 處理 url，首先在項目settings文件的同一目錄下，建立一個叫utils的package，而後在這個包裏建立一個md5文件； 使用以前先從hashlib中導入md5，把hashlib中md5()實例化，而後用update傳入url，再用 hexdigest() 提取摘要。還能夠使用isinstance()來判判斷傳入值編碼類型，使用encode()方法將unicode編碼轉換成其餘編碼的字符串等；

from hashlib import md5
def get_md5(url):
    if isinstance(url, str):
        # 先轉化爲字節碼
        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()
    # 添加圖片路徑到item中
    image_path = scrapy.Field()
    # 加頁面的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. 將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):
        # 獲取a標籤的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數據模型進行落地，數據持久化
        yield item

6.建立JsonSavePipeline，用於寫入item到文件中

import codecs
import json

class JsonSavePipeline:
    def process_item(self, item, spider):
        # 將spider中返回的item轉化爲字典
        file = codecs.open('blog.json', mode='a')
        dict_item = dict(item)
        # 將字典json化
        line = json.dumps(dict_item, ensure_ascii=False) + '\n'
        # 寫入到文件
        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,

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