python - 为什么此解析器找不到使用 namespace 前缀的 XML 标记的内容？

Question

我有这个 XML 代码，取自 this link :

<?xml version="1.0" encoding="UTF-8"?>
<rss xmlns:dc="http://purl.org/dc/elements/1.1/" xmlns:media="http://search.yahoo.com/mrss/" xmlns:atom="http://www.w3.org/2005/Atom" xmlns:nyt="http://www.nytimes.com/namespaces/rss/2.0" version="2.0">
  <channel>
    <item>
      <title>‘This Did Not Go Well’: Inside PG&amp;E’s Blackout Control Room</title>
      <dc:creator>Ivan Penn</dc:creator>
      <pubDate>Sat, 12 Oct 2019 17:03:11 +0000</pubDate>
    </item>
  </channel>
</rss>

当我尝试使用 lxml 解析它时并遵循 documentation for xpath and XML namespaces ，解析器找到标题(不使用命名空间)，但找不到作者/创建者，这会:

from lxml import html

xml = """
<?xml version="1.0" encoding="UTF-8"?>
<rss xmlns:dc="http://purl.org/dc/elements/1.1/" xmlns:media="http://search.yahoo.com/mrss/" xmlns:atom="http://www.w3.org/2005/Atom" xmlns:nyt="http://www.nytimes.com/namespaces/rss/2.0" version="2.0">
  <channel>
    <item>
      <title>‘This Did Not Go Well’: Inside PG&amp;E’s Blackout Control Room</title>
      <dc:creator>Ivan Penn</dc:creator>
      <pubDate>Sat, 12 Oct 2019 17:03:11 +0000</pubDate>
    </item>
  </channel>
</rss>
"""


rss = html.fromstring(xml)
items = rss.xpath("//item")
for item in items:
    title = item.xpath("title")[0].text_content().strip()
    print(title)

    ns = {"dc" : "http://purl.org/dc/elements/1.1/"}
    authors = item.xpath("dc:creator", namespaces = ns)
    print(authors)

此代码打印:

This Did Not Go Well’: Inside PG&E’s Blackout Control Room []

由于它正确地找到了标题标签的内容，我认为它找到了个人 <item>标签。我将命名空间传递给 xpath 的方式有问题吗？ ？

编辑:无论我是否使用尾部斜杠，结果都是相同的，即

ns = {"dc" : "http://purl.org/dc/elements/1.1/"}
ns = {"dc" : "http://purl.org/dc/elements/1.1"}

Answer 1

HTML 解析器忽略命名空间。这是 Running HTML doctests 中的最后一句话lxml 文档中的部分:

The HTML parser notably ignores namespaces and some other XMLisms.

Another part文档说:

Also note that the HTML parser is meant to parse HTML documents. For XHTML documents, use the XML parser, which is namespace aware.

如果你改变它就会起作用

authors = item.xpath("dc:creator", namespaces = ns)

至

authors = item.xpath("creator")

但由于 RSS 不是 HTML，请考虑使用 XML 解析器(from lxml import etree)。