在Python语言中使用ElementTree发出命名空间规范

Question

我正在尝试发出一个包含XML声明和名称空间的XML文件，其中包含元素树。下面是我的示例代码：

from xml.etree import ElementTree as ET
ET.register_namespace('com',"http://www.company.com") #some name

# build a tree structure
root = ET.Element("STUFF")
body = ET.SubElement(root, "MORE_STUFF")
body.text = "STUFF EVERYWHERE!"

# wrap it in an ElementTree instance, and save as XML
tree = ET.ElementTree(root)

tree.write("page.xml",
           xml_declaration=True,
           method="xml" )

但是，既不显示<?xml标记，也不显示任何名称空间/前缀信息。我有点迷惑了。

Answer 1

尽管docs另有说明，但我只能通过同时指定xml_declaration和编码来获得<?xml>声明。

您必须在已注册的名称空间中声明节点，才能在文件中的节点上获得名称空间。以下是您的代码的修复版本：

from xml.etree import ElementTree as ET
ET.register_namespace('com',"http://www.company.com") #some name

# build a tree structure
root = ET.Element("{http://www.company.com}STUFF")
body = ET.SubElement(root, "{http://www.company.com}MORE_STUFF")
body.text = "STUFF EVERYWHERE!"

# wrap it in an ElementTree instance, and save as XML
tree = ET.ElementTree(root)

tree.write("page.xml",
           xml_declaration=True,encoding='utf-8',
           method="xml")

输出(page.xml)

<?xml version='1.0' encoding='utf-8'?><com:STUFF xmlns:com="http://www.company.com"><com:MORE_STUFF>STUFF EVERYWHERE!</com:MORE_STUFF></com:STUFF>

ElementTree的打印效果也不好。下面是打印得很漂亮的输出：

<?xml version='1.0' encoding='utf-8'?>
<com:STUFF xmlns:com="http://www.company.com">
    <com:MORE_STUFF>STUFF EVERYWHERE!</com:MORE_STUFF>
</com:STUFF>

您还可以声明一个默认名称空间，而不需要注册一个：

from xml.etree import ElementTree as ET

# build a tree structure
root = ET.Element("{http://www.company.com}STUFF")
body = ET.SubElement(root, "{http://www.company.com}MORE_STUFF")
body.text = "STUFF EVERYWHERE!"

# wrap it in an ElementTree instance, and save as XML
tree = ET.ElementTree(root)

tree.write("page.xml",
           xml_declaration=True,encoding='utf-8',
           method="xml",default_namespace='http://www.company.com')

输出(精美字体间距是我的)

<?xml version='1.0' encoding='utf-8'?>
<STUFF xmlns="http://www.company.com">
    <MORE_STUFF>STUFF EVERYWHERE!</MORE_STUFF>
</STUFF>

Answer 2

我从来没有能够以编程的方式从元素树库中获得<?xml标记，所以我建议您尝试这样做。

from xml.etree import ElementTree as ET
root = ET.Element("STUFF")
root.set('com','http://www.company.com')
body = ET.SubElement(root, "MORE_STUFF")
body.text = "STUFF EVERYWHERE!"

f = open('page.xml', 'w')
f.write('<?xml version="1.0" encoding="UTF-8"?>' + ET.tostring(root))
f.close()

非std lib python ElementTree实现可能有不同的方式来指定名称空间，所以如果您决定迁移到lxml，那么声明这些名称空间的方式也会有所不同。