我试图使用Python3.x从Amazon上获取评论，但一无所获

我正试图从亚马逊获取所有评论。当我运行下面的代码时，它返回空列表，没有任何错误。我不明白为什么。你能帮帮我吗

from __future__ import unicode_literals

import requests
from scrapy.selector import Selector

def fetch_page(url):
    r = requests.get(url)
    return r.text 

def  review_positive(url):
    #html = fetch_page(url)
    sel = Selector(text = url)
    review =  sel.css(' .a-section review').extract()
    return review


print (review_positive('https://www.amazon.com/Apple-iPhone-Unlocked-GB-Packaging/product-reviews/B01DAJT1AW/ref=cm_cr_arp_d_viewpnt_lft?ie=UTF8&showViewpoints=1&sortBy=helpful&filterByStar=positive&pageNumber=1'))

---

在类之间的CSS选择器中不应该有空格。相反，请使用

分隔类：

.css('.a-section.review').extract()

一旦解决了该问题，选择器将正常工作：

In [6]: rev = response.css('.a-section.review').extract()

In [7]: len(rev)
Out[7]: 10

In [8]: rev = response.css('.a-section review').extract()

In [9]: len(rev)
Out[9]: 0