python - 使用 lxml 解析 DTD 时出错

Question

我正在尝试编写一个验证脚本来根据 NITF DTD 验证 XML，http://www.iptc.org/std/NITF/3.4/specification/dtd/nitf-3-4.dtd .基于this post我提出了以下简单脚本来验证 NITF XML 文档。 Bellow 是我在运行脚本时收到的错误消息，它不是很具有描述性并且很难调试。感谢您的帮助。

#!/usr/bin/env python


def main():
    from lxml import etree, objectify
    from StringIO import StringIO

    f = open('nitf_test.xml')
    xml_doc = f.read()
    f.close()

    f = open('nitf-3-4.dtd')
    dtd_doc = f.read()
    f.close()

    dtd = etree.DTD(StringIO(dtd_doc))
    tree = objectify.parse(StringIO(xml_doc))
    dtd.validate(tree)


if __name__ == '__main__':

    main()

回溯错误信息:

Traceback (most recent call last):
  File "./test_nitf_doc.py", line 23, in <module>
    main()
  File "./test_nitf_doc.py", line 16, in main
    dtd = etree.DTD(StringIO(dtd_doc))
  File "dtd.pxi", line 43, in lxml.etree.DTD.__init__ (src/lxml/lxml.etree.c:126056)
  File "dtd.pxi", line 117, in lxml.etree._parseDtdFromFilelike (src/lxml/lxml.etree.c:126727)
lxml.etree.DTDParseError: error parsing DTD

如果我改变行:

dtd = etree.DTD(StringIO(dtd_doc))

收件人:

dtd = etree.DTD(dtd_doc)

我得到的错误是:

lxml.etree.DTDParseError: failed to load external entity "NULL"

Answer 1

我查看了 nitf-3-4.dtd 并发现它引用了一个外部模块 xhtml-ruby-1.mod ，它可以是 downloaded at this link 。这需要出现在当前目录中，以便 DTD 解析器可以加载它。

完整的工作示例(假设您手边有有效的 NITF 文档):

% wget http://www.iptc.org/std/NITF/3.4/specification/dtd/nitf-3-4.dtd
% wget http://www.iptc.org/std/NITF/3.4/specification/dtd/xhtml-ruby-1.mod

Python代码:

from lxml import etree, objectify
dtd = etree.DTD(open('nitf-3-4.dtd', 'rb'))
tree = objectify.parse(open('nitf_test.xml', 'rb'))
print dtd.validate(tree)

输出:

% python nitf_test.py
True