python-dir.bbclass question when using multiple versions of Python.

python-dir.bbclass question when using multiple versions of Python.

[Rodney Lott]

Hi, there.

I am looking at the latest revision from org.openembedded.dev: 

=========================================
rlott@rlott-desktop:~/git/oe/oe-meta/classes$ git log -1
commit ad112ee1ce53dfaf3fa2d7a10a79f724c8dd6335
Author: Martin Jansa <Martin.Jansa@gmail.com>
Date:   Thu Aug 12 22:28:35 2010 +0200

    task-shr-feed: add supertux-qvga wesnoth
    
    Signed-off-by: Martin Jansa <Martin.Jansa@gmail.com>
rlott@rlott-desktop:~/git/oe/oe-meta/classes$ git br
  master
* org.openembedded.dev
  org.openembedded.stable
==========================================

I am looking at the classes/python-dir.bbclass function:

==========================================
def python_dir(d):
    import os, bb
    staging_incdir = bb.data.getVar( "STAGING_INCDIR", d, 1 )
    for majmin in "2.6 2.5 2.4 2.3".split():
        if os.path.exists( "%s/python%s" % ( staging_incdir, majmin ) ): return "python%s" % majmin
    if not "python-native" in bb.data.getVar( "DEPENDS", d, 1 ).split():
        raise Exception("No Python in STAGING_INCDIR. Forgot to build python-native?")
    return "INVALID"

PYTHON_DIR = "${@python_dir(d)}"
PYTHON_SITEPACKAGES_DIR = "${libdir}/${PYTHON_DIR}/site-packages"
==========================================

Now, if I am reading this correctly, it would seem that the logic of this function is as follows, "Look for python directories in STAGING_INCDIR, starting from 2.6 downward, and use the first one I find."

This works if one is only using one version of Python.  Let's say one is using Python 2.5 and Python 2.6 (i.e. for two different applications) and I am in the process of building something that I need to work with Python 2.6, it will set PYTHON_DIR to point to /usr/lib/python2.6/site-packages, which isn't what I want.

So, my question is this:  Is it OE's assumption that one is only to use a single version of Python within one build (i.e. one tmp directory), or should it work with multiple Pythons per temp directory?  If it is the later, then it would seem to me that using STAGING_INCDIR to determine the Python version isn't a good idea and that the Python version one is using should be derived (somehow) from the PREFERRED_VERSION_python and PREFERRED_VERSION_python-native settings.  

Just an observation and I would like to know which paradigm is the correct one.

TIA.

Rodney Lott

Re: python-dir.bbclass question when using multiple versions of Python.

[Chris Larson]

On Thu, Aug 12, 2010 at 2:29 PM, Rodney Lott <rlott@evertz.com> wrote:

> Hi, there.
>
> I am looking at the latest revision from org.openembedded.dev:
>
> =========================================
> rlott@rlott-desktop:~/git/oe/oe-meta/classes$ git log -1
> commit ad112ee1ce53dfaf3fa2d7a10a79f724c8dd6335
> Author: Martin Jansa <Martin.Jansa@gmail.com>
> Date:   Thu Aug 12 22:28:35 2010 +0200
>
>    task-shr-feed: add supertux-qvga wesnoth
>
>    Signed-off-by: Martin Jansa <Martin.Jansa@gmail.com>
> rlott@rlott-desktop:~/git/oe/oe-meta/classes$ git br
>  master
> * org.openembedded.dev
>  org.openembedded.stable
> ==========================================
>
> I am looking at the classes/python-dir.bbclass function:
>
> ==========================================
> def python_dir(d):
>    import os, bb
>    staging_incdir = bb.data.getVar( "STAGING_INCDIR", d, 1 )
>    for majmin in "2.6 2.5 2.4 2.3".split():
>        if os.path.exists( "%s/python%s" % ( staging_incdir, majmin ) ):
> return "python%s" % majmin
>    if not "python-native" in bb.data.getVar( "DEPENDS", d, 1 ).split():
>        raise Exception("No Python in STAGING_INCDIR. Forgot to build
> python-native?")
>    return "INVALID"
>
> PYTHON_DIR = "${@python_dir(d)}"
> PYTHON_SITEPACKAGES_DIR = "${libdir}/${PYTHON_DIR}/site-packages"
> ==========================================
>
> Now, if I am reading this correctly, it would seem that the logic of this
> function is as follows, "Look for python directories in STAGING_INCDIR,
> starting from 2.6 downward, and use the first one I find."
>
> This works if one is only using one version of Python.  Let's say one is
> using Python 2.5 and Python 2.6 (i.e. for two different applications) and I
> am in the process of building something that I need to work with Python 2.6,
> it will set PYTHON_DIR to point to /usr/lib/python2.6/site-packages, which
> isn't what I want.
>
> So, my question is this:  Is it OE's assumption that one is only to use a
> single version of Python within one build (i.e. one tmp directory), or
> should it work with multiple Pythons per temp directory?  If it is the
> later, then it would seem to me that using STAGING_INCDIR to determine the
> Python version isn't a good idea and that the Python version one is using
> should be derived (somehow) from the PREFERRED_VERSION_python and
> PREFERRED_VERSION_python-native settings


Building multiple versions of *anything* in a single build is prone to
failure and problems.  Headers will step on one another's toes in staging
depending on the build order, etc.  Python is no exception.
-- 
Christopher Larson
clarson at kergoth dot com
Founder - BitBake, OpenEmbedded, OpenZaurus
Maintainer - Tslib
Senior Software Engineer, Mentor Graphics