Re: [xml] Building Python wrappers for libxml2 and libxslt under Python 2.2

[Tres Seaver <tseaver zope com>]

On Tue, 2002-09-10 at 17:21, Daniel Veillard wrote:
> On Tue, Sep 10, 2002 at 12:24:12PM -0400, Tres Seaver wrote:
> > On a box where libxml2 and libxslt are installed via RPM, I need to
> > build the Python wrappers for a Python which is *not* the system
> > Python.  Under Python 2.1.3, this recipe works:
> >
> >   $ cd opt/libxml2-python-2.4.24
> >   $ ../../bin/python setup.py build install
> >
> > Under Python 2.2.1, the same compile fails, because each C module tries
> > to include the header file, "config.h".  My guess is that the 2.1.3
> > builds are working (or at least appearing to) because Python's own
> > include directory contains a config.h;  for Python >= 2.2, that file was
> > renamed pyconfig.h.  In either case, the Python.h includes the
> > appropriate file, and so including it directly has no effect.
>
>   Hum, right ... BTW my RPM spec file (and Red Hat ones since they are
> the same :-) build libxml2-python and libxslt-python with modules
> for all the python installations found at RPM generation time.

I need to use the wrappers for a Python which RPM doesn't know about (we
build a custom one in order to guarantee that it has the configuration
we need).

> And 
> this does not use the setup.py stuff (make rpm in the directory does it).
>
> > Is this header file supposed to be one generated by the libxml2/libxslt
> > configure process, rather than the Python one?  If so, how will this
> > configuration be available in an environment where the base packages
> > were compiled via RPM?  config.h is not installed into
> > /usr/include/libxml2, for instance.
>
>   Possibly including <libxml/xmlversion.h> should do it.

I started to look at this again last night.

I tried building the Python wrappers via distutils after commenting out
the '#include <config.h>' lines;  the compile succeeds, which suggests
that the lines are not needed.  Can you suggest a way to test that the
wrappers are OK?  The wrapper modules import without problems.

> BTW I was unable to find how to lookup/associate Include directories
> from the setup.py scripts. If libxml2 is installed in /usr it's easy
> to spot but otherwise one would have to run xml-config, extract the
> parameter and use them from the script. And for Windows I have really
> no idea how to do this.

'distutils.sysconfig' has an API, 'get_config_vars', which can tell you
where the Python configuration expects to find "system" includes:

  >>> from distutils.sysconfig import get_config_vars
  >>> get_config_vars( 'INCLUDEDIR' )
  ['/usr/include']

The PyXML package allows setting the path for the Expat parser via a
'--with-expat=' parameter to setup.py:

  for arg in args:
      if string.find(arg, '--with-libexpat=') == 0:
          LIBEXPAT = string.split(arg, '=')[1]
          sys.argv.remove(arg)

That package then passes that path through to the builder step for
the Expat wrapper module:

  expat_prefix = get_expat_prefix()

  sources = ['extensions/pyexpat.c']
  if expat_prefix:
      define_macros = [('HAVE_EXPAT_H', None)]
      include_dirs = [os.path.join(expat_prefix, "include")]
      libraries = ['expat']
      library_dirs = [os.path.join(expat_prefix, "lib")]
  # ...
    
  ext_modules.append(
      Extension(xml('.parsers.pyexpat'),
                define_macros=define_macros,
                include_dirs=include_dirs,
                library_dirs=library_dirs,
                libraries=libraries,
                extra_link_args=LDFLAGS,
                sources=sources
              ))

I think that running 'xml-config' via 'os.popen' would work:

  >>> foo = os.popen( 'xml-config --cflags' )
  >>> bar = foo.read()
  >>> print bar
  -I/usr/include/gnome-xml

Tres.
-- 
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Tres Seaver                                tseaver zope com
Zope Corporation      "Zope Dealers"       http://www.zope.com