使用lxml编写，即使pretty_print=Tru时也不发出空白

Question

我使用lxml库来读取xml模板，插入/更改一些元素，并保存生成的xml。我使用etree.Element和etree.SubElement方法动态创建的元素之一：

tree = etree.parse(r'xml_archive\templates\metadata_template_pts.xml')
root = tree.getroot()

stream = []
for element in root.iter():
    if isinstance(element.tag, basestring):
        stream.append(element.tag)

        # Find "keywords" element and insert a new "theme" element
        if element.tag == 'keywords' and 'theme' not in stream:
            theme = etree.Element('theme')
            themekt = etree.SubElement(theme, 'themekt').text = 'None'
            for tk in themekeys:
                themekey = etree.SubElement(theme, 'themekey').text = tk
            element.insert(0, theme)

很好地打印到屏幕上print etree.tostring(theme, pretty_print=True)：

^{pr2}$

但是，当使用etree.ElementTree(root).write(out_xml_file, method='xml', pretty_print=True)写出xml时，该元素在输出文件中变平：

<theme><themekt>None</themekt><themekey>Hydrogeology</themekey><themekey>Stratigraphy</themekey><themekey>Floridan aquifer system</themekey><themekey>Geology</themekey><themekey>Regional Groundwater Availability Study</themekey><themekey>USGS</themekey><themekey>United States Geological Survey</themekey><themekey>thickness</themekey><themekey>altitude</themekey><themekey>extent</themekey><themekey>regions</themekey><themekey>upper confining unit</themekey><themekey>FAS</themekey><themekey>base</themekey><themekey>geologic units</themekey><themekey>geology</themekey><themekey>extent</themekey><themekey>inlandWaters</themekey></theme>

文件的其余部分写得很好，但是这个特殊的元素引起了（纯粹是美学上的）麻烦。你知道我做错了什么吗？在

---

下面是模板xml文件中的标记片段（另存为“模板.xml“在底部使用代码段运行）。标签的扁平化只在我解析现有文件并插入新元素时发生，而不是在使用lxml从头创建xml时发生。在

<?xml version="1.0" encoding="UTF-8"?>
<?xml-stylesheet type="text/xsl" href="fgdc_classic.xsl"?>
<metadata xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="http://water.usgs.gov/GIS/metadata/usgswrd/fgdc-std-001-1998.xsd">
    <keywords>
       <theme>
            <themekt>ISO 19115 Topic Categories</themekt>
            <themekey>environment</themekey>
            <themekey>geoscientificInformation</themekey>
            <themekey>inlandWaters</themekey>
        </theme>
        <place>
            <placekt>None</placekt>
            <placekey>Florida</placekey>
            <placekey>Georgia</placekey>
            <placekey>Alabama</placekey>
            <placekey>South Carolina</placekey>
        </place>
    </keywords>

</metadata>

下面是要与标记片段（上图）一起使用的代码片段：

# Create new theme element to insert into root
themekeys = ['Hydrogeology', 'Stratigraphy', 'inlandWaters']

tree = etree.parse(r'template.xml')
root = tree.getroot()

stream = []
for element in root.iter():
    if isinstance(element.tag, basestring):
        stream.append(element.tag)

        # Edit theme keywords
        if element.tag == 'keywords':
            theme = etree.Element('theme')
            themekt = etree.SubElement(theme, 'themekt').text = 'None'
            for tk in themekeys:
                themekey = etree.SubElement(theme, 'themekey').text = tk
            element.insert(0, theme)

# Write XML to new file
out_xml_file = 'test.xml'
etree.ElementTree(root).write(out_xml_file, method='xml', pretty_print=True)
with open(out_xml_file, 'r') as f:
    lines = f.readlines()

with open(out_xml_file, 'w') as f:
    f.write('<?xml version="1.0" encoding="UTF-8"?>\n')
    for line in lines:
        f.write(line)

Answer 1

如果替换这一行：

tree = etree.parse(r'template.xml')

有了这些线条：

^{pr2}$

然后它会像预期的那样工作。诀窍是使用一个XMLParser，它将remove_blank_text选项设置为True。任何现有的可忽略空白都将被删除，因此不会中断后续的漂亮打印。在