问题
I'm trying to learn how to scrape web pages and in the tutorial I'm using the code below is throwing this error:
lxml.etree.XPathEvalError: Invalid predicate
The website I'm querying is (don't judge me, it was the one used in the training vid :/ ): https://itunes.apple.com/us/app/candy-crush-saga/id553834731
The xpath string that causes the error is here:
links = tree.xpath('//div[@class="center-stack"//*/a[@class="name"]/@href')
I'm using the LXML and requests libraries.
If you need any additional info I'm happy to provide!
回答1:
print(tree.xpath('//div[@class="center-stack"]//*/a[@class="name"]/@href'))
You were missing a closing ] after "center-stack".
You can also just pull the a[@class="name"] tags from div[@class="content"]
tree.xpath('//div[@class="content"]//a[@class="name"]/@href')
Both will give you the hrefs you want:
In [19]: import requests
In [20]: from lxml.html import fromstring
In [21]: r = requests.get("https://itunes.apple.com/us/app/candy-crush-saga/id553834731")
In [22]: tree = fromstring(r.content)
In [23]: a = tree.xpath('//div[@class="content"]//a[@class="name"]/@href')
In [24]: b = tree.xpath('//div[@class="center-stack"]//*/a[@class="name"]/@href')
In [25]: print(a == b)
True
In [26]: print(a)
['https://itunes.apple.com/us/app/word-search-puzzles/id609067187?mt=8', 'https://itunes.apple.com/us/app/cookie-jam/id727296976?mt=8', 'https://itunes.apple.com/us/app/jewel-mania/id561326449?mt=8', 'https://itunes.apple.com/us/app/jelly-splash/id645949180?mt=8', 'https://itunes.apple.com/us/app/bubble-island/id531354582?mt=8']
In [27]: print(b)
['https://itunes.apple.com/us/app/word-search-puzzles/id609067187?mt=8', 'https://itunes.apple.com/us/app/cookie-jam/id727296976?mt=8', 'https://itunes.apple.com/us/app/jewel-mania/id561326449?mt=8', 'https://itunes.apple.com/us/app/jelly-splash/id645949180?mt=8', 'https://itunes.apple.com/us/app/bubble-island/id531354582?mt=8']
来源：https://stackoverflow.com/questions/36449369/python-xpath-lxml-etree-xpathevalerror-invalid-predicate