在Python中使用ElementTree发出命名空间规范

Question

我正在尝试使用element-tree生成一个包含XML声明和命名空间的XML文件。以下是我的示例代码：

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，生成的文件里既没有出现<?xml标签，也没有任何命名空间或前缀信息。我对此感到有些困惑。

Answer 1

我从来没办法通过代码把 <?xml 标签从元素树库中提取出来，所以我建议你可以试试下面这种方法。

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()

不同的非标准库的 Python ElementTree 实现可能在指定命名空间时有不同的方式，所以如果你决定换用 lxml，声明这些命名空间的方法也会有所不同。

Answer 2

虽然文档上说的可能不一样，但我发现只有在同时指定了xml_declaration和编码后，才能得到一个<?xml>声明。

你需要在你注册的命名空间中声明节点，才能在文件中的节点上看到这个命名空间。下面是你代码的修正版本：

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也不会自动美化输出。这里是经过美化的输出：

<?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>

---

你还可以声明一个默认的命名空间，这样就不需要再注册一个了：

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 (美化后的格式是我自己调整的)

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