Looking for portable what to determine directory where extensions are installed?

Tom Epperly tepperly at llnl.gov
Thu Nov 5 18:20:28 CET 2009

I work on a language interoperability tool, Babel 
https://computation.llnl.gov/casc/components/components.html; and I need 
a portable way to determine the directory where Python extension modules 
are installed by distutils (i.e., lib or lib64) to resolve this issue: 

For example, I will invoke "python setup.py install 
--prefix=/home/foo/_inst --exec-prefix=/home/foo/_inst", and it usually 
installs the extensions in either 
/home/foo/_inst/lib/python2.5/site-packages or 
/home/foo/_inst/lib64/python2.5/site-packages. Initially, I did the 
following to determine where the extensions actually got installed:

# assume exec_prefix=/home/foo/_inst
# assume python_version=`python -c 'import sys; print sys.version' | sed '1s/^\(...\).*/\1/g;1q'`

This worked fine until I started running on 64-bit Python machines where 
the correct result was


The first 64-bit machine I was using seemed to have this patch: 
http://bugs.python.org/file14726/Python-2.6.2-multilib.patch, so I 
amended my script to the following:

pylib=`$PYTHON -c "import sys; print sys.__dict__.get('lib','lib')"`

However, this approach doesn't work with Fedora Core 12 prerelease or 
some other 64-bit Linux distributions. They don't define "sys.lib".

I thought distutils.sysconfig.get_python_lib() might be helpful, but it 
returns "/usr/lib/python2.6/site-packages" even on the system where 
"/usr/lib64/python2.6/site-packages" is the right answer.

Is there a canonical, Pythonic way to determine whether an installation 
of Python uses "lib" or "lib64"?  Or is there a way to determine the 
full path of where distutils will install extensions relative to the 
specified exec prefix?


Tom Epperly

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