ElementTree and xsi to xmlns conversion?

[Matthew Thorley]

Why does ElementTree.parse convert my xsi to an xmlns?

When I do this
from elementtree import ElementTree

# Sample xml
mgac ="""
<mgac xmlns="http://www.chpc.utah.edu/~baites/mgacML"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://www.chpc.utah.edu/~baites/mgacML
http://www.chpc.utah.edu/~baites/mgacML/mgac.xsd"><cluster
name="Si4H"></cluster></mgac>
"""

xml = ElementTree.fromstring(mgac)
ElementTree.tostring(xml)

I get this
'<ns0:mgac ns1:schemaLocation="http://www.chpc.utah.edu/~baites/mgacML
http://www.chpc.utah.edu/~baites/mgacML/mgac.xsd"
xmlns:ns0="http://www.chpc.utah.edu/~baites/mgacML"
xmlns:ns1="http://www.w3.org/2001/XMLSchema-instance"><ns0:cluster
name="Si4H" /></ns0:mgac>'

The xsi is gone and has been replaced by a new xmlns, which is also NOT
inherited by the child elements.

ElementTree.tostring(xml.getchildren()[0])

'<ns0:cluster name="Si4H"
xmlns:ns0="http://www.chpc.utah.edu/~baites/mgacML" />'

If some one could please explain where I'm off I'd really appreciate it.
I need to use xsi: to validate the document, and I'm not sure how to
pass it on to the children when I reformat the doc.

Thanks
-Matthew

[Fredrik Lundh]

Matthew Thorley wrote:
> Why does ElementTree.parse convert my xsi to an xmlns?

because it is a namespace prefix, perhaps?

> When I do this
> from elementtree import ElementTree
>
> # Sample xml
> mgac ="""
> <mgac xmlns="http://www.chpc.utah.edu/~baites/mgacML"
> xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
> xsi:schemaLocation="http://www.chpc.utah.edu/~baites/mgacML
> http://www.chpc.utah.edu/~baites/mgacML/mgac.xsd"><cluster
> name="Si4H"></cluster></mgac>
> """
>
> xml = ElementTree.fromstring(mgac)
> ElementTree.tostring(xml)
>
> I get this
> '<ns0:mgac ns1:schemaLocation="http://www.chpc.utah.edu/~baites/mgacML
> http://www.chpc.utah.edu/~baites/mgacML/mgac.xsd"
> xmlns:ns0="http://www.chpc.utah.edu/~baites/mgacML"
> xmlns:ns1="http://www.w3.org/2001/XMLSchema-instance"><ns0:cluster
> name="Si4H" /></ns0:mgac>'
>
> The xsi is gone and has been replaced by a new xmlns, which is also NOT
> inherited by the child elements.

the xsi is a namespace prefix, which maps to a namespace URI. the child element
doesn't use that namespace, so there's no need to add a namespace declaration.

> ElementTree.tostring(xml.getchildren()[0])
>
> '<ns0:cluster name="Si4H"
> xmlns:ns0="http://www.chpc.utah.edu/~baites/mgacML" />'
>
> If some one could please explain where I'm off I'd really appreciate it.
> I need to use xsi: to validate the document

are you sure? the prefix shouldn't matter; it's the namespace URI that's important.
if you're writing code that depends on the namespace prefix rather than the name-
space URI, you're not using namespaces correctly. when it comes to namespaces,
elementtree forces you to do things the right way:

http://www.jclark.com/xml/xmlns.htm

(unfortunately, the XML schema authors didn't understand namespaces so they
messed things up:
http://www.w3.org/2001/tag/doc/qnameids-2002-04-30
to work around this, see oren's message about how to control the namespace/prefix
mapping. in worst case, you can manually insert xsi:-attributes in the tree, and rely on
the fact that the default writer only modifies universal names)

</F>

[Matthew Thorley]

Thanks for the reply I am understanding it better now. Please forgive my
ignorance. So the xsi is just an arbitrary name space prefix, I get that
now. And it make sense to me why it gets converted to an xmlns.

What I really need to know is why it is not inherited by the child
elements? From what I an told, I need the second namespace, so that I
can point to the schema, so that I can validate the document.

Is that the wrong way to link to the schema? Can I force both namespaces
to be inherited by the child elements?

Thanks for all the help
-Matthew