Re: {pkgsrc-users} Re: Proposed patch for python 2.[56] to enable elementtree

[Brian de Alwis <bsd%cs.ubc.ca@localhost>]

On 9-Sep-2009, at 4:41 PM, Joerg Sonnenberger wrote:
> On Wed, Sep 09, 2009 at 01:04:58PM -0400, Brian de Alwis wrote:
> > Attached is a patch to simply install the _elementtree module Pythons
> > 2.5 and 2.6 and deprecate the textproc/py-elementtree package.
>
> The patch seems very incomplete :) Are you sure that it doesn't use
> expat? I seem to remember that it contains references to that at the
> very least...


No, I'm not sure, but I'm fairly certain it's more complete than the  
current situation :-)  My attempt at deprecating py-elementtree may be  
bogus and require more work (more below).  And see the note about  
expat further below.

Basically, this patch attempts to correct the broken  
xml.etree.cElementTree left by the lang/python2[56] packages.  These  
packages essentially do a full install *except* for the shared  
libraries corresponding to some major modules.  The Python source code  
for to those modules *is* installed by the python2[56] packages.   
Their shared libraries are actually built and installed by  
corresponding py-* packages instead.

So for example, if you install python26, you'll find the ElementTree  
and cElementTree code installed.

    $ pkg_info -qL python26 | grep -i xml.etree
    /usr/pkg/lib/python2.6/test/test_xml_etree.py
    /usr/pkg/lib/python2.6/test/test_xml_etree.pyc
    /usr/pkg/lib/python2.6/test/test_xml_etree.pyo
    /usr/pkg/lib/python2.6/test/test_xml_etree_c.py
    /usr/pkg/lib/python2.6/test/test_xml_etree_c.pyc
    /usr/pkg/lib/python2.6/test/test_xml_etree_c.pyo
    /usr/pkg/lib/python2.6/xml/etree/ElementInclude.py
    /usr/pkg/lib/python2.6/xml/etree/ElementInclude.pyc
    /usr/pkg/lib/python2.6/xml/etree/ElementInclude.pyo
    /usr/pkg/lib/python2.6/xml/etree/ElementPath.py
    /usr/pkg/lib/python2.6/xml/etree/ElementPath.pyc
    /usr/pkg/lib/python2.6/xml/etree/ElementPath.pyo
    /usr/pkg/lib/python2.6/xml/etree/ElementTree.py
    /usr/pkg/lib/python2.6/xml/etree/ElementTree.pyc
    /usr/pkg/lib/python2.6/xml/etree/ElementTree.pyo
    /usr/pkg/lib/python2.6/xml/etree/__init__.py
    /usr/pkg/lib/python2.6/xml/etree/__init__.pyc
    /usr/pkg/lib/python2.6/xml/etree/__init__.pyo
    /usr/pkg/lib/python2.6/xml/etree/cElementTree.py
    /usr/pkg/lib/python2.6/xml/etree/cElementTree.pyc
    /usr/pkg/lib/python2.6/xml/etree/cElementTree.pyo

And attempting to use the ElementTree code will succeed, even without  
the py-elementtree package installed.  But trying to use  
xml.etree.cElementTree will fail though as the _elementtree module  
isn't installed:

    $ python2.6
    Python 2.6.2 (r262:71600, Sep 10 2009, 14:33:58)
    [GCC 4.0.1 (Apple Inc. build 5490)] on darwin
    Type "help", "copyright", "credits" or "license" for more  
information.
    >>> import xml.etree.ElementTree
    >>> import xml.etree.cElementTree
    Traceback (most recent call last):
      File "<stdin>", line 1, in <module>
      File "/usr/pkg/lib/python2.6/xml/etree/cElementTree.py", line  
3, in <module>
        from _elementtree import *
    ImportError: No module named _elementtree
    >>>

Note that it is attempting to load the _elementtree module.  This  
module is *not* installed by the py-elementtree package because it  
installs the external ElementTree packages.  So pkgsrc's python2[56]  
leave a broken xml.etree.cElementTree.  My patch causes the  
_elementtree shared library to be installed by default; it changes  
little else.

My patch's attempt at deprecating py-elementtree may be unnecessary  
since the in-tree versions have been prefixed with xml.etree; they  
should be able to co-exist.

My motivation for this is that I use devel/bzr, which thrives when  
able to use cElementTree.  Bzr first looks for the in-tree xml.etree.c? 
ElementTree, and then falls back to the external c?ElementTree.  But  
bzr does support Python 2.4, and thus should require the textproc/py- 
elementtree package (I've only ever tried it with Python 2.5 though,  
so it wasn't a concern).

Re: expat: the ElementTree code does seem to try to load expat for its  
XMLTreeBuilder class, but does provides a fallback  
SimpleXMLTreeBuilder that works without expat.  Anyways, it seems we  
can use the expat module even without the py-expat package installed!

Brian.

--
"Amusement to an observing mind is study." - Benjamin Disraeli