Question

我正在尝试使用lxml从锚链接中找到所有图像（.png，.bmp，.jpg）和可执行文件（.exe）。从这个similar thread，接受的答案建议做这样的事情：

png = tree.xpath("//div/ul/li//a[ends-with(@href, '.png')]")
bmp = tree.xpath("//div/ul/li//a[ends-with(@href, '.bmp')]")
jpg = tree.xpath("//div/ul/li//a[ends-with(@href, '.jpg')]")
exe = tree.xpath("//div/ul/li//a[ends-with(@href, '.exe')]")

然而，我不断收到此错误：

Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "lxml.etree.pyx", line 2095, in lxml.etree._ElementTree.xpath (src/lxml/lxml.etree.c:53597)
  File "xpath.pxi", line 373, in lxml.etree.XPathDocumentEvaluator.__call__ (src/lxml/lxml.etree.c:134052)
  File "xpath.pxi", line 241, in lxml.etree._XPathEvaluatorBase._handle_result (src/lxml/lxml.etree.c:132625)
  File "xpath.pxi", line 226, in lxml.etree._XPathEvaluatorBase._raise_eval_error (src/lxml/lxml.etree.c:132453)
lxml.etree.XPathEvalError: Unregistered function

我正在通过pip运行lxml 3.2.4。

此外，有没有一种方法可以使用xpath并一次指定所有四个文件扩展名，而不是为每个文件扩展名定义xpath 4次？

Answer 1

ends-with是为XPath 2.0，XQuery 1.0和XSLT 2.0定义的函数，而lxml仅支持XPath 1.0，XSLT 1.0和EXSLT扩展。所以你不能使用这个功能。该文档为here和here。

您可以在XPATH中使用正则表达式。以下是返回与正则表达式匹配的节点的示例代码：

regexpNS = 'http://exslt.org/regular-expressions'
tree.xpath("//a[re:test(@href, '(png|bmp|jpg|exe)$')]", namespaces={'re':regexpNS}")

以下是类似问题Python, XPath: Find all links to images和regular-expressions-in-xpath

Answer 2

我认为这是外部库无法识别ends-with功能的问题。 documentation discusses working with links。{{3}}。我认为更好的解决方案是：

from urlparse import urlparse
tree.make_links_absolute(base_href='http://example.com/')
links = []
for i in tree.iterlinks():
    url = urlparse(i[2])  # ensures you are getting the remote file path
    if url.path.endswith('.png') or url.path.endswith('.exe') ... :
        # there are other ways you could filter the links here
        links.append(i[2])

lxml - 查找具有特定扩展名的所有链接

2 个答案: