[lxml-dev] redundant namespace declarations (was: pretty-printing)

Hi, Albert Brandl wrote:

I've posted a question about pretty-printing some time ago. Now I finally found the time to construct an example.

The problem occurs with the following code:

nsmap = dict (foo="http://foo.org", bar = "http://bar.org") e = Element("{http://foo.org}somefoo", nsmap = nsmap) s = Element("{http://bar.org}somebar", nsmap = nsmap) e.append(s1) et = ElementTree(e) et.write("foo.xml", pretty_print = True)

This code creates the following XML file:

http://foo.org" xmlns:bar="http://bar.org"> http://foo.org" xmlns:bar="http://bar.org"/>

I get the same here.

The problem is that "bar:somebar" redundantly declares the namespaces for "foo" and "bar", which affects both the readability and the size of the XML file.

True. Doesn't affect it's semantics, though.

If the element "s" is appended to "e" by using the SubElement function instead of "append", the content of the XML file looks like I'd expect:

http://foo.org" xmlns:bar="http://bar.org"> bar:somebar/

That case is easier to handle than the above, so lxml/libxml2 optimises it.

Is this a known bug?

It's known - though not really a bug but rather an inconvenience. Currently, we use a function in libxml2 called xmlReconciliateNs() to fix the namespaces when merging trees. This function shows the above behaviour. To fix this, we'd have to implement our own version, which is a bit tricky and just wasn't important enough to try to get right so far. Note that even libxml2 had a (minor) bug up to version 2.6.26 here, so it's really not trivial to get this kind of thing right. Stefan