scrapy 将抓取内容中的图片下载到本地并替换内容中的原始图片

def parse_article(self, response):
    item = response.meta['item']
    item['title'] = response.xpath("//div[@id='content']//h1[@class='entry-title']/text()").extract()[0]
    article_imgs = response.xpath("//div[@id='content']/article/div[@class='entry-content']//img")
    for img in article_imgs:
        img_src = img.xpath("/@src").extract()[0]
        file_name = os.path.basename(img_src)
        real_name = file_name.split('.')[-2]
        print("图片名称", real_name)
        save_path = 'images/shopify/' + str(real_name)
        print("保存路径", save_path)
        local_path = self.save_img(img_src, save_path)
        http_img_path = urljoin('http://www.tiangr.com', '/wp_content/uploads/' + local_path)
        print("替换路径", http_img_path)
        ####################
        到这里之后不知道该怎么替换原来的图片路径。
        ####################

    item['content'] = response.xpath("//div[@id='content']/article/div[@class='entry-content']").extract()[0]
    item['cimage_urls'] = response.xpath("//div[@id='content']//header[@class='entry-header']/img//@src").extract()     # 提取图片链接
    yield item

def save_img(self, img_url, file_name):
    """
    保存图片
    :param img_url 图片地址
    :param file_name 文件名称
    :return:
    """
    image_path = img_url.split('.')
    extension = image_path.pop()
    if len(extension) > 3:
        extension = 'jpg'
    img_url = urljoin('http://dingyue.nosdn.127.net', img_url)
    u = urllib.request.urlopen(img_url)
    data = u.read()
    f = open(file_name + '.' + extension, 'wb')
    f.write(data)
    f.close()
    return file_name + '.' + extension