[XML-SIG] add Namespace Defaulting to ElementTree.write()

[Stefan Behnel]

Peter Hoffmann wrote:
> As I somtimes have to look  at or even edit xml markup generated by
> ElementTree, it would be a lot easier if ElementTree could use
> Namespace Defaultig  as described in http://www.w3.org/TR/REC-xml-names/#defaulting
> 
> Here is an example what I mean:
> ### raw input
> <book xmlns='urn:loc.gov:books'
>       xmlns:isbn='urn:ISBN:0-395-36341-6'>
>     <title>Cheaper by the Dozen</title>
>     <isbn:number>1568491379</isbn:number>
> </book>
> 
> ### normal ElementTree output
> <ns0:book xmlns:ns0="urn:loc.gov:books">
>     <ns0:title>Cheaper by the Dozen</ns0:title>
>     <ns1:number xmlns:ns1="urn:ISBN:0-395-36341-6">1568491379</
> ns1:number>
> </ns0:book>
> 
> ### with Patch/set default_namespace="urn:loc.gov:books"
> <book xmlns="urn:loc.gov:books">
>     <title>Cheaper by the Dozen</title>
>     <ns1:number xmlns:ns1="urn:ISBN:0-395-36341-6">1568491379</
> ns1:number>
> </book>


lxml.etree has been using a property called "nsmap" since the beginning, which
is already more generic than just a default namespace. If ElementTree wants to
adopt such a feature, I'd be happy if it could keep up compatibility from its
own side here.

Stefan