Hi, Jan-Christoph Klie schrieb am 06.11.18 um 11:54:

I am currently serializing some largish XML files in Python with lxml. I want to use the incremental writer for that. My XML format heavily relies on namespaces and attributes. When I run the following code

from io import BytesIO

from lxml import etree

sink = BytesIO()

nsmap = { 'test': 'http://test.org', 'foo': 'http://foo.org', 'bar': 'http://bar.org', }

with etree.xmlfile(sink) as xf: with xf.element("test:testElement", nsmap=nsmap): name = etree.QName(nsmap["foo"], "fooElement") elem = etree.Element(name)

xf.write(elem)

print(sink.getvalue().decode('utf-8'))

then I get the following output:

<test:testElement xmlns:bar="http://bar.org" xmlns:foo="http://foo.org" xmlns:test="http://test.org"> <ns0:fooElement xmlns:ns0="http://foo.org"/> </test:testElement>

As you can see, the namespace for `foo` is repeated and not my prefix:

<ns0:fooElement xmlns:ns0="http://foo.org"/>

How do I make it so lxml only adds the namespace in the root and children use the correct prefix from there?

That's not currently supported. It could be, but it's not easy, since the incremental serialiser is separate from the normal Element serialiser, and both are used here, and have their own separate namespace handling. But as Charlie Clark already said, it doesn't matter. Any namespace aware XML parser will happily handle these redundant declarations.

2) Specifying the `nsmap` in the element:

elem = etree.Element(name, nsmap=nsmap)

yields

<foo:fooElement xmlns:bar="http://bar.org" xmlns:foo="http://foo.org" xmlns:test="http://test.org"/>

for the `fooElement`.

You could selectively declare only the namespaces you need. But again, it really doesn't matter. XML parsers will be happy with this.

I also looked in the documentation and source code of lxml, but it is Cython so really hard to read and search. The context manager of `xf.element` does not return the element. e.g.

with xf.element('foo:fooElement') as e: print(e)

prints `None`.

At that point, the element has already been serialised, so there is nothing left to do with it. Stefan