可以告诉ElementTree保留属性的顺序吗？ [英] Can ElementTree be told to preserve the order of attributes?

问题描述

我使用ElementTree在python中编写了一个相当简单的过滤器，以调整某些xml文件的上下文。它或多或少地起作用。

I've written a fairly simple filter in python using ElementTree to munge the contexts of some xml files. And it works, more or less.

但是它重新排序了各种标签的属性，我希望它不要这样做。

But it reorders the attributes of various tags, and I'd like it to not do that.

有人知道我可以扔出一个开关来使其保持指定的顺序吗？

Does anyone know a switch I can throw to make it keep them in specified order?

我正在使用一个粒子物理工具，该工具具有基于xml文件的复杂但奇怪的配置系统。以这种方式设置的许多事物中包括各种静态数据文件的路径。这些路径被硬编码到现有的xml中，没有基于环境变量设置或更改它们的功能，在我们的本地安装中，它们必然位于不同的位置。

I'm working with and on a particle physics tool that has a complex, but oddly limited configuration system based on xml files. Among the many things setup that way are the paths to various static data files. These paths are hardcoded into the existing xml and there are no facilities for setting or varying them based on environment variables, and in our local installation they are necessarily in a different place.

这不是灾难，因为我们正在使用的源代码控制和构建控制工具相结合，使我们可以使用本地副本隐藏某些文件。但是，即使考虑到数据字段是静态的，xml也不是静态的，所以我写了一个脚本来修复路径，但是由于属性重排，本地版本和主版本之间的差异比必需的要难读。

This isn't a disaster because the combined source- and build-control tool we're using allows us to shadow certain files with local copies. But even thought the data fields are static the xml isn't, so I've written a script for fixing the paths, but with the attribute rearrangement diffs between the local and master versions are harder to read than necessary.

这是我第一次带ElementTree旋转（只有我的第五或第六个python项目），所以也许我只是做错了。

This is my first time taking ElementTree for a spin (and only my fifth or sixth python project) so maybe I'm just doing it wrong.

为简单起见，代码摘要如下：

Abstracted for simplicity the code looks like this:

tree = elementtree.ElementTree.parse(inputfile)
i = tree.getiterator()
for e in i:
    e.text = filter(e.text)
tree.write(outputfile)

合理还是愚蠢？

相关链接：

• 如何使用Python xml.sax获取元素属性列表的顺序？


• 使用minidom修改时保留属性顺序

• How can I get the order of an element attribute list using Python xml.sax?
• Preserve order of attributes when modifying with minidom

推荐答案

在@bobince的答案和这两个帮助下（设置属性顺序，覆盖模块方法）

With help from @bobince's answer and these two (setting attribute order, overriding module methods)

我设法修补了这只猴子，它很脏，我建议使用另一个更好地处理这种情况的模块，但是当不可能：

I managed to get this monkey patched it's dirty and I'd suggest using another module that better handles this scenario but when that isn't a possibility:

# =======================================================================
# Monkey patch ElementTree
import xml.etree.ElementTree as ET

def _serialize_xml(write, elem, encoding, qnames, namespaces):
    tag = elem.tag
    text = elem.text
    if tag is ET.Comment:
        write("<!--%s-->" % ET._encode(text, encoding))
    elif tag is ET.ProcessingInstruction:
        write("<?%s?>" % ET._encode(text, encoding))
    else:
        tag = qnames[tag]
        if tag is None:
            if text:
                write(ET._escape_cdata(text, encoding))
            for e in elem:
                _serialize_xml(write, e, encoding, qnames, None)
        else:
            write("<" + tag)
            items = elem.items()
            if items or namespaces:
                if namespaces:
                    for v, k in sorted(namespaces.items(),
                                       key=lambda x: x[1]):  # sort on prefix
                        if k:
                            k = ":" + k
                        write(" xmlns%s=\"%s\"" % (
                            k.encode(encoding),
                            ET._escape_attrib(v, encoding)
                            ))
                #for k, v in sorted(items):  # lexical order
                for k, v in items: # Monkey patch
                    if isinstance(k, ET.QName):
                        k = k.text
                    if isinstance(v, ET.QName):
                        v = qnames[v.text]
                    else:
                        v = ET._escape_attrib(v, encoding)
                    write(" %s=\"%s\"" % (qnames[k], v))
            if text or len(elem):
                write(">")
                if text:
                    write(ET._escape_cdata(text, encoding))
                for e in elem:
                    _serialize_xml(write, e, encoding, qnames, None)
                write("</" + tag + ">")
            else:
                write(" />")
    if elem.tail:
        write(ET._escape_cdata(elem.tail, encoding))

ET._serialize_xml = _serialize_xml

from collections import OrderedDict

class OrderedXMLTreeBuilder(ET.XMLTreeBuilder):
    def _start_list(self, tag, attrib_in):
        fixname = self._fixname
        tag = fixname(tag)
        attrib = OrderedDict()
        if attrib_in:
            for i in range(0, len(attrib_in), 2):
                attrib[fixname(attrib_in[i])] = self._fixtext(attrib_in[i+1])
        return self._target.start(tag, attrib)

# =======================================================================

然后在您的代码中：

tree = ET.parse(pathToFile, OrderedXMLTreeBuilder())

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