使用lxml解析DTD时出错

Question

我正在尝试编写一个验证脚本,该脚本将针对NITF DTD验证XML,http: //www.iptc.org/std/NITF/3.4/specification/dtd/nitf-3-4.dtd .基于这篇文章,我提出了以下简单的脚本来验证NITF XML文档.Bellow是我在运行脚本时得到的错误消息,它不是很具描述性并且很难调试.任何帮助表示赞赏.

#!/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()

回溯错误消息:

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

如果我换行:

dtd = etree.DTD(StringIO(dtd_doc))

至:

dtd = etree.DTD(dtd_doc)

我得到的错误是:

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

Answer 1

我看了一眼,nitf-3-4.dtd发现它引用了一个外部模块xhtml-ruby-1.mod,可以在这个链接上下载.这需要存在于当前目录中,以便DTD解析器可以加载它.

完整的工作示例(假设您有一个有效的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