奇怪的lxml行为 [英] Strange lxml behavior

问题描述

我手动创建xml，然后尝试使用xsd方案对其进行验证.最初不会通过验证，但是如果我将xml转换为字符串然后返回-那么新的xml将通过验证.

I create xml manually and then try to validate it with xsd scheme. Validation doesn't pass at first, but if I convert xml to a string and back - then new xml passes validation.

from lxml import etree

xsd = etree.fromstring("""
<schema xmlns="http://www.w3.org/2001/XMLSchema" targetNamespace="some_namespace">
    <element name="el"></element>
</schema>""")
schema = etree.XMLSchema(xsd)

xml1 = etree.Element('el', nsmap={None: "some_namespace"})
xml2 = etree.fromstring(etree.tostring(xml1))

schema.assertValid(xml2)  # this passes
schema.assertValid(xml1)  # this fails

我看到xml1和xml2具有不同的标记:

I see that xml1 and xml2 have different tags:

print xml1.tag  # --> el
print xml2.tag  # --> {some_namespace}el

但是，为什么xml1和xml2有如此大的区别?看起来它们应该是相同的.

But why xml1 and xml2 have such a difference? Looks like they should be the same.

推荐答案

在此处创建 el 元素(无名称空间):

Here you create an el element (no namespace):

xml1 = etree.Element('el', nsmap={None: "some_namespace"})

使用 nsmap 参数不会将元素绑定到名称空间；它只是提供了序列化的映射.

Using a nsmap parameter does not bind the element to a namespace; it just provides a mapping for serialization.

执行 etree.tostring(xml1)时，序列化行为开始".解析序列化结果后， xml2 是一个 {some_namespace} el 元素，而不是 el .

When etree.tostring(xml1) is executed, the serialization behaviour "kicks in". When the serialized result has been parsed, xml2 is an {some_namespace}el element instead of el.

要使其正常运行，请将行更改为:

To make it work, change the line to:

xml1 = etree.Element('{some_namespace}el', nsmap={None: "some_namespace"})

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