python lxml以预定义的顺序写入文件

Question

我想编写以下lxml etree 子元素：

<ElementProtocolat0x3803048>,
<ElementStudyEventDefat0x3803108>,
<ElementFormDefat0x3803248>,
<ElementItemGroupDefat0x38032c8>,
<ElementClinicalDataat0x3803408>,
<ElementItemGroupDataat0x38035c8>,
<ElementFormDefat0x38036c8>,

以预定义的顺序到我的 odm xml 文件。IE

<ElementProtocolat0x3803048>,
<ElementStudyEventDefat0x3803108>,
<ElementFormDefat0x3803248>,
<ElementFormDefat0x38036c8>,
<ElementItemGroupDefat0x38032c8>,
<ElementItemGroupDataat0x38035c8>,
<ElementClinicalDataat0x3803408>,
....

有没有办法对元素进行排序，即使用预定义的列表？

predefined_order = ['Protocol', 'StudyEventDef','FormDef','ItemGroupDef','ItemDef','CodeList']

Answer 1

此示例演示：

• 如何读入 XML 文件，
• 元素是一个列表，可以这样操作
• 如何根据可匹配子字符串的预定义顺序对列表进行排序
• 如何写出一个 XML 文件

from lxml import etree
import re

# Parse the XML and find the root
with open('input.xml') as input_file:
    tree = etree.parse(input_file)
root = tree.getroot()

# Find the list to sort and sort it
some_arbitrary_expression_to_find_the_list = '.'
element_list = tree.xpath(some_arbitrary_expression_to_find_the_list)[0]

predefined_order = [
    'Protocol',
    'StudyEventDef',
    'FormDef',
    'ItemGroupDef',
    'ItemGroupData',
    'ItemDef',
    'CodeList',
    'ClinicalData']
filter = re.compile(r'Element(.*)at0x.*')

element_list[:] = sorted(
    element_list[:],
    key = lambda x: predefined_order.index(filter.match(x.tag).group(1)))

# Write the XML to the output file
with open('output.xml', 'w') as output_file:
    output_file.write(etree.tostring(tree, pretty_print = True))

样本输入：

<stuff>
<ElementProtocolat0x3803048 />
<ElementStudyEventDefat0x3803108 />
<ElementFormDefat0x3803248 />
<ElementItemGroupDefat0x38032c8>Random Text</ElementItemGroupDefat0x38032c8>
<ElementClinicalDataat0x3803408 />
<ElementItemGroupDataat0x38035c8><tag1><tag2 attr="random tags"/></tag1></ElementItemGroupDataat0x38035c8>
<ElementFormDefat0x38036c8 />
</stuff>

输出：

<stuff>
<ElementProtocolat0x3803048/>
<ElementStudyEventDefat0x3803108/>
<ElementFormDefat0x3803248/>
<ElementFormDefat0x38036c8/>
<ElementItemGroupDefat0x38032c8>Random Text</ElementItemGroupDefat0x38032c8>
<ElementItemGroupDataat0x38035c8><tag1><tag2 attr="random tags"/></tag1></ElementItemGroupDataat0x38035c8>
<ElementClinicalDataat0x3803408/>
</stuff>